Remove SupportsWeakPtr inheritance from GLES2Decoder

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 3e43f7c2ab6edf1ce080cfffbdc3885fcbb55f57..cceeb6138d94ff5a7063de02ba8f9ed17fdadd61 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder.h
+++ b/gpu/command_buffer/service/gles2_cmd_decoder.h
@@ -82,8 +82,7 @@ typedef base::Callback<void(const std::string& key,
 
 // This class implements the AsyncAPIInterface interface, decoding GLES2
 // commands and calling GL.
-class GPU_EXPORT GLES2Decoder : public base::SupportsWeakPtr<GLES2Decoder>,
-                                public CommonDecoder {
+class GPU_EXPORT GLES2Decoder : public CommonDecoder {
  public:
   typedef error::Error Error;
   typedef base::Callback<void(uint64_t release)> FenceSyncReleaseCallback;
@@ -126,6 +125,8 @@ class GPU_EXPORT GLES2Decoder : public base::SupportsWeakPtr<GLES2Decoder>,
     log_commands_ = log_commands;
   }
 
+  virtual base::WeakPtr<GLES2Decoder> AsWeakPtr() = 0;
+
   // Initializes the graphics context. Can create an offscreen
   // decoder with a frame buffer that can be referenced from the parent.
   // Takes ownership of GLContext.