Add a second unsafe ES3 API in command buffer.

gpu/command_buffer/client/gles2_implementation_autogen.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This file is auto-generated from
 // gpu/command_buffer/build_gles2_cmd_buffer.py
 // It's formatted by clang-format using chromium coding style:
 //    clang-format -i -style=chromium filename
 // DO NOT EDIT!
 
@@ skipping 76 matching lines @@
 void CompressedTexSubImage2D(GLenum target,
                              GLint level,
                              GLint xoffset,
                              GLint yoffset,
                              GLsizei width,
                              GLsizei height,
                              GLenum format,
                              GLsizei imageSize,
                              const void* data) override;
 
+void CopyBufferSubData(GLenum readtarget,
+                       GLenum writetarget,
+                       GLintptr readoffset,
+                       GLintptr writeoffset,
+                       GLsizeiptr size) override;
+
 void CopyTexImage2D(GLenum target,
                     GLint level,
                     GLenum internalformat,
                     GLint x,
                     GLint y,
                     GLsizei width,
                     GLsizei height,
                     GLint border) override;
 
 void CopyTexSubImage2D(GLenum target,
@@ skipping 597 matching lines @@
                                   GLfloat uv_width,
                                   GLfloat uv_height) override;
 
 void MatrixLoadfCHROMIUM(GLenum matrixMode, const GLfloat* m) override;
 
 void MatrixLoadIdentityCHROMIUM(GLenum matrixMode) override;
 
 void BlendBarrierKHR() override;
 
 #endif  // GPU_COMMAND_BUFFER_CLIENT_GLES2_IMPLEMENTATION_AUTOGEN_H_