Add missing generics in MethodDescriptor

-------------
Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=72155290
diff --git a/core/src/main/java/com/google/net/stubby/MethodDescriptor.java b/core/src/main/java/com/google/net/stubby/MethodDescriptor.java
index a9ab6b4..482b42f 100644
--- a/core/src/main/java/com/google/net/stubby/MethodDescriptor.java
+++ b/core/src/main/java/com/google/net/stubby/MethodDescriptor.java
@@ -112,7 +112,7 @@
   /**
    * Create a new descriptor with a different timeout
    */
-  public MethodDescriptor withTimeout(long timeout, TimeUnit unit) {
+  public MethodDescriptor<RequestT, ResponseT> withTimeout(long timeout, TimeUnit unit) {
     return new MethodDescriptor<RequestT, ResponseT>(type, name, unit.toMicros(timeout),
         requestMarshaller, responseMarshaller, headers);
   }
@@ -120,7 +120,8 @@
   /**
    * Create a new descriptor with an additional bound header.
    */
-  public MethodDescriptor withHeader(String headerName, Provider<String> headerValueProvider) {
+  public MethodDescriptor<RequestT, ResponseT> withHeader(String headerName,
+      Provider<String> headerValueProvider) {
     return new MethodDescriptor<RequestT, ResponseT>(type, name, timeoutMicros,
         requestMarshaller, responseMarshaller,
         ImmutableMap.<String, Provider<String>>builder().