Separate ServerCall binding utilities per method type.

This gives us more flexibility in API changes in the future.

Unary call and server streaming call should call the flow-control method
call.request() only once. Previously it was called whenever a request
arrives, which is wrong. Now it's fixed.

Resolves #436
diff --git a/compiler/src/java_plugin/cpp/java_generator.cpp b/compiler/src/java_plugin/cpp/java_generator.cpp
index 5795157..bac19ca 100644
--- a/compiler/src/java_plugin/cpp/java_generator.cpp
+++ b/compiler/src/java_plugin/cpp/java_generator.cpp
@@ -512,14 +512,27 @@
     (*vars)["input_type"] = MessageFullJavaName(method->input_type());
     (*vars)["output_type"] = MessageFullJavaName(method->output_type());
     bool client_streaming = method->client_streaming();
+    bool server_streaming = method->server_streaming();
     if (client_streaming) {
-      (*vars)["calls_method"] = "asyncStreamingRequestCall";
-      (*vars)["invocation_class"] =
-          "io.grpc.stub.ServerCalls.StreamingRequestMethod";
+      if (server_streaming) {
+        (*vars)["calls_method"] = "asyncDuplexStreamingCall";
+        (*vars)["invocation_class"] =
+            "io.grpc.stub.ServerCalls.DuplexStreamingMethod";
+      } else {
+        (*vars)["calls_method"] = "asyncClientStreamingCall";
+        (*vars)["invocation_class"] =
+            "io.grpc.stub.ServerCalls.ClientStreamingMethod";
+      }
     } else {
-      (*vars)["calls_method"] = "asyncUnaryRequestCall";
-      (*vars)["invocation_class"] =
-          "io.grpc.stub.ServerCalls.UnaryRequestMethod";
+      if (server_streaming) {
+        (*vars)["calls_method"] = "asyncServerStreamingCall";
+        (*vars)["invocation_class"] =
+            "io.grpc.stub.ServerCalls.ServerStreamingMethod";
+      } else {
+        (*vars)["calls_method"] = "asyncUnaryCall";
+        (*vars)["invocation_class"] =
+            "io.grpc.stub.ServerCalls.UnaryMethod";
+      }
     }
     p->Print(*vars, ".addMethod($ServerMethodDefinition$.create(\n");
     p->Indent();
@@ -647,9 +660,13 @@
       "import static "
       "io.grpc.stub.ClientCalls.unaryFutureCall;\n"
       "import static "
-      "io.grpc.stub.ServerCalls.asyncUnaryRequestCall;\n"
+      "io.grpc.stub.ServerCalls.asyncUnaryCall;\n"
       "import static "
-      "io.grpc.stub.ServerCalls.asyncStreamingRequestCall;\n\n");
+      "io.grpc.stub.ServerCalls.asyncServerStreamingCall;\n"
+      "import static "
+      "io.grpc.stub.ServerCalls.asyncClientStreamingCall;\n"
+      "import static "
+      "io.grpc.stub.ServerCalls.asyncDuplexStreamingCall;\n\n");
   if (generate_nano) {
     p->Print("import java.io.IOException;\n\n");
   }
diff --git a/compiler/src/test/golden/TestService.java.txt b/compiler/src/test/golden/TestService.java.txt
index a8b4f47..13d92f3 100644
--- a/compiler/src/test/golden/TestService.java.txt
+++ b/compiler/src/test/golden/TestService.java.txt
@@ -7,8 +7,10 @@
 import static io.grpc.stub.ClientCalls.blockingUnaryCall;
 import static io.grpc.stub.ClientCalls.blockingServerStreamingCall;
 import static io.grpc.stub.ClientCalls.unaryFutureCall;
-import static io.grpc.stub.ServerCalls.asyncUnaryRequestCall;
-import static io.grpc.stub.ServerCalls.asyncStreamingRequestCall;
+import static io.grpc.stub.ServerCalls.asyncUnaryCall;
+import static io.grpc.stub.ServerCalls.asyncServerStreamingCall;
+import static io.grpc.stub.ServerCalls.asyncClientStreamingCall;
+import static io.grpc.stub.ServerCalls.asyncDuplexStreamingCall;
 
 @javax.annotation.Generated("by gRPC proto compiler")
 public class TestServiceGrpc {
@@ -289,8 +291,8 @@
     return io.grpc.ServerServiceDefinition.builder("grpc.testing.TestService")
       .addMethod(io.grpc.ServerMethodDefinition.create(
           METHOD_UNARY_CALL,
-          asyncUnaryRequestCall(
-            new io.grpc.stub.ServerCalls.UnaryRequestMethod<
+          asyncUnaryCall(
+            new io.grpc.stub.ServerCalls.UnaryMethod<
                 io.grpc.testing.integration.Test.SimpleRequest,
                 io.grpc.testing.integration.Test.SimpleResponse>() {
               @java.lang.Override
@@ -302,8 +304,8 @@
             })))
       .addMethod(io.grpc.ServerMethodDefinition.create(
           METHOD_STREAMING_OUTPUT_CALL,
-          asyncUnaryRequestCall(
-            new io.grpc.stub.ServerCalls.UnaryRequestMethod<
+          asyncServerStreamingCall(
+            new io.grpc.stub.ServerCalls.ServerStreamingMethod<
                 io.grpc.testing.integration.Test.StreamingOutputCallRequest,
                 io.grpc.testing.integration.Test.StreamingOutputCallResponse>() {
               @java.lang.Override
@@ -315,8 +317,8 @@
             })))
       .addMethod(io.grpc.ServerMethodDefinition.create(
           METHOD_STREAMING_INPUT_CALL,
-          asyncStreamingRequestCall(
-            new io.grpc.stub.ServerCalls.StreamingRequestMethod<
+          asyncClientStreamingCall(
+            new io.grpc.stub.ServerCalls.ClientStreamingMethod<
                 io.grpc.testing.integration.Test.StreamingInputCallRequest,
                 io.grpc.testing.integration.Test.StreamingInputCallResponse>() {
               @java.lang.Override
@@ -327,8 +329,8 @@
             })))
       .addMethod(io.grpc.ServerMethodDefinition.create(
           METHOD_FULL_DUPLEX_CALL,
-          asyncStreamingRequestCall(
-            new io.grpc.stub.ServerCalls.StreamingRequestMethod<
+          asyncDuplexStreamingCall(
+            new io.grpc.stub.ServerCalls.DuplexStreamingMethod<
                 io.grpc.testing.integration.Test.StreamingOutputCallRequest,
                 io.grpc.testing.integration.Test.StreamingOutputCallResponse>() {
               @java.lang.Override
@@ -339,8 +341,8 @@
             })))
       .addMethod(io.grpc.ServerMethodDefinition.create(
           METHOD_HALF_DUPLEX_CALL,
-          asyncStreamingRequestCall(
-            new io.grpc.stub.ServerCalls.StreamingRequestMethod<
+          asyncDuplexStreamingCall(
+            new io.grpc.stub.ServerCalls.DuplexStreamingMethod<
                 io.grpc.testing.integration.Test.StreamingOutputCallRequest,
                 io.grpc.testing.integration.Test.StreamingOutputCallResponse>() {
               @java.lang.Override
diff --git a/compiler/src/test/golden/TestServiceNano.java.txt b/compiler/src/test/golden/TestServiceNano.java.txt
index 114f671..07e98a8 100644
--- a/compiler/src/test/golden/TestServiceNano.java.txt
+++ b/compiler/src/test/golden/TestServiceNano.java.txt
@@ -7,8 +7,10 @@
 import static io.grpc.stub.ClientCalls.blockingUnaryCall;
 import static io.grpc.stub.ClientCalls.blockingServerStreamingCall;
 import static io.grpc.stub.ClientCalls.unaryFutureCall;
-import static io.grpc.stub.ServerCalls.asyncUnaryRequestCall;
-import static io.grpc.stub.ServerCalls.asyncStreamingRequestCall;
+import static io.grpc.stub.ServerCalls.asyncUnaryCall;
+import static io.grpc.stub.ServerCalls.asyncServerStreamingCall;
+import static io.grpc.stub.ServerCalls.asyncClientStreamingCall;
+import static io.grpc.stub.ServerCalls.asyncDuplexStreamingCall;
 
 import java.io.IOException;
 
@@ -351,8 +353,8 @@
     return io.grpc.ServerServiceDefinition.builder("grpc.testing.TestService")
       .addMethod(io.grpc.ServerMethodDefinition.create(
           METHOD_UNARY_CALL,
-          asyncUnaryRequestCall(
-            new io.grpc.stub.ServerCalls.UnaryRequestMethod<
+          asyncUnaryCall(
+            new io.grpc.stub.ServerCalls.UnaryMethod<
                 io.grpc.testing.integration.Test.SimpleRequest,
                 io.grpc.testing.integration.Test.SimpleResponse>() {
               @java.lang.Override
@@ -364,8 +366,8 @@
             })))
       .addMethod(io.grpc.ServerMethodDefinition.create(
           METHOD_STREAMING_OUTPUT_CALL,
-          asyncUnaryRequestCall(
-            new io.grpc.stub.ServerCalls.UnaryRequestMethod<
+          asyncServerStreamingCall(
+            new io.grpc.stub.ServerCalls.ServerStreamingMethod<
                 io.grpc.testing.integration.Test.StreamingOutputCallRequest,
                 io.grpc.testing.integration.Test.StreamingOutputCallResponse>() {
               @java.lang.Override
@@ -377,8 +379,8 @@
             })))
       .addMethod(io.grpc.ServerMethodDefinition.create(
           METHOD_STREAMING_INPUT_CALL,
-          asyncStreamingRequestCall(
-            new io.grpc.stub.ServerCalls.StreamingRequestMethod<
+          asyncClientStreamingCall(
+            new io.grpc.stub.ServerCalls.ClientStreamingMethod<
                 io.grpc.testing.integration.Test.StreamingInputCallRequest,
                 io.grpc.testing.integration.Test.StreamingInputCallResponse>() {
               @java.lang.Override
@@ -389,8 +391,8 @@
             })))
       .addMethod(io.grpc.ServerMethodDefinition.create(
           METHOD_FULL_DUPLEX_CALL,
-          asyncStreamingRequestCall(
-            new io.grpc.stub.ServerCalls.StreamingRequestMethod<
+          asyncDuplexStreamingCall(
+            new io.grpc.stub.ServerCalls.DuplexStreamingMethod<
                 io.grpc.testing.integration.Test.StreamingOutputCallRequest,
                 io.grpc.testing.integration.Test.StreamingOutputCallResponse>() {
               @java.lang.Override
@@ -401,8 +403,8 @@
             })))
       .addMethod(io.grpc.ServerMethodDefinition.create(
           METHOD_HALF_DUPLEX_CALL,
-          asyncStreamingRequestCall(
-            new io.grpc.stub.ServerCalls.StreamingRequestMethod<
+          asyncDuplexStreamingCall(
+            new io.grpc.stub.ServerCalls.DuplexStreamingMethod<
                 io.grpc.testing.integration.Test.StreamingOutputCallRequest,
                 io.grpc.testing.integration.Test.StreamingOutputCallResponse>() {
               @java.lang.Override