implement getBufferSubDataAsync prototype

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 1149 matching lines @@
 void BindFragmentInputLocationCHROMIUM(GLuint program,
                                        GLint location,
                                        const char* name) override;
 
 void ProgramPathFragmentInputGenCHROMIUM(GLuint program,
                                          GLint location,
                                          GLenum genMode,
                                          GLint components,
                                          const GLfloat* coeffs) override;
 
+void* GetBufferSubDataAsyncCHROMIUM(GLenum target,
+                                    GLintptr offset,
+                                    GLsizeiptr size) override;
+
 void CoverageModulationCHROMIUM(GLenum components) override;
 
 GLenum GetGraphicsResetStatusKHR() override;
 
 void BlendBarrierKHR() override;
 
 void ApplyScreenSpaceAntialiasingCHROMIUM() override;
 
 void BindFragDataLocationIndexedEXT(GLuint program,
                                     GLuint colorNumber,
@@ skipping 10 matching lines @@
     GLint location,
     GLboolean transpose,
     const GLfloat* transform) override;
 
 void SwapBuffersWithDamageCHROMIUM(GLint x,
                                    GLint y,
                                    GLint width,
                                    GLint height) override;
 
 #endif  // GPU_COMMAND_BUFFER_CLIENT_GLES2_IMPLEMENTATION_AUTOGEN_H_