Move logic to write to stdout into CodeWriter

This will allow us to reuse it when we write C++ code.
I think this will mostly come in handy for debugging.

While here, rename the helper functions in accordance with the style
guide.

Test: unittests
Bug: 24220933

Change-Id: I269eb4a0dda10588c2ae77b7c8f2b00e50e70047
diff --git a/generate_java.cpp b/generate_java.cpp
index 5626d3d..868783c 100644
--- a/generate_java.cpp
+++ b/generate_java.cpp
@@ -78,22 +78,7 @@
         document->originalSrc = originalSrc;
         document->classes.push_back(cl);
 
-//    printf("outputting... filename=%s\n", filename.c_str());
-    FILE* to;
-    if (filename == "-") {
-        to = stdout;
-    } else {
-       /* open file in binary mode to ensure that the tool produces the
-        * same output on all platforms !!
-        */
-        to = fopen(filename.c_str(), "wb");
-        if (to == NULL) {
-            fprintf(stderr, "unable to open %s for write\n", filename.c_str());
-            return 1;
-        }
-    }
-
-    CodeWriterPtr code_writer = get_file_writer(to);
+    CodeWriterPtr code_writer = GetFileWriter(filename);
     document->Write(code_writer.get());
 
     return 0;