Use the extensions generated by FeatureInfo in the passthrough cmd decoder.

gpu/command_buffer/service/gles2_cmd_decoder_passthrough.h

Index: gpu/command_buffer/service/gles2_cmd_decoder_passthrough.h
diff --git a/gpu/command_buffer/service/gles2_cmd_decoder_passthrough.h b/gpu/command_buffer/service/gles2_cmd_decoder_passthrough.h
index b69598763f309804dd3c04ce113184437af2a6ff..6f3fb5ca11da02dd6d35488ebba82f91ad9b481c 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder_passthrough.h
+++ b/gpu/command_buffer/service/gles2_cmd_decoder_passthrough.h
@@ -278,8 +278,6 @@ class GLES2DecoderPassthroughImpl : public GLES2Decoder {
                                                       GLsizei length,
                                                       GLint* params);
 
-  void BuildExtensionsString();
-
   void InsertError(GLenum error, const std::string& message);
   GLenum PopError();
   bool FlushErrors();
@@ -378,9 +376,6 @@ class GLES2DecoderPassthroughImpl : public GLES2Decoder {
 
   std::set<GLenum> errors_;
 
-  std::vector<std::string> emulated_extensions_;
-  std::string extension_string_;
-
   // Cache of scratch memory
   std::vector<uint8_t> scratch_memory_;