Implement TransformFeedbackManager in GPU command buffer.

gpu/command_buffer/service/gles2_cmd_decoder.h

Index: gpu/command_buffer/service/gles2_cmd_decoder.h
diff --git a/gpu/command_buffer/service/gles2_cmd_decoder.h b/gpu/command_buffer/service/gles2_cmd_decoder.h
index 668fbcf540052e4742380af7290e3756ef372fa8..b5465ab5ab3c91bb50049b09cf2ed880747bc888 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder.h
+++ b/gpu/command_buffer/service/gles2_cmd_decoder.h
@@ -43,6 +43,7 @@ class ImageManager;
 class Logger;
 class QueryManager;
 class Texture;
+class TransformFeedbackManager;
 class VertexArrayManager;
 struct ContextState;
 
@@ -207,6 +208,9 @@ class GPU_EXPORT GLES2Decoder : public base::SupportsWeakPtr<GLES2Decoder>,
   // Gets the QueryManager for this context.
   virtual QueryManager* GetQueryManager() = 0;
 
+  // Gets the TransformFeedbackManager for this context.
+  virtual TransformFeedbackManager* GetTransformFeedbackManager() = 0;
+
   // Gets the VertexArrayManager for this context.
   virtual VertexArrayManager* GetVertexArrayManager() = 0;