(not for commit) Simplified multi-threaded Ganesh with lock on Flush only.

gpu/command_buffer/client/gles2_implementation.h

Index: gpu/command_buffer/client/gles2_implementation.h
diff --git a/gpu/command_buffer/client/gles2_implementation.h b/gpu/command_buffer/client/gles2_implementation.h
index 470200e898bd222b527a4ac88a6c1062ccf9f27e..a06d1ba5ba48024f985eb3eb9d911d309ef6e04d 100644
--- a/gpu/command_buffer/client/gles2_implementation.h
+++ b/gpu/command_buffer/client/gles2_implementation.h
@@ -194,6 +194,9 @@ class GLES2_IMPL_EXPORT GLES2Implementation
   // this file instead of having to edit some template or the code generator.
   #include "gpu/command_buffer/client/gles2_implementation_autogen.h"
 
+  void SetSafeFlushPoint() override;
+  void SafeFlush() override;
+
   void DisableVertexAttribArray(GLuint index) override;
   void EnableVertexAttribArray(GLuint index) override;
   void GetVertexAttribfv(GLuint index, GLenum pname, GLfloat* params) override;