Add a mechanism for command buffer to conditionally allow ES3 enums.

gpu/command_buffer/common/gles2_cmd_utils_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 4478 matching lines @@
       {GL_BUFFER_SIZE, "GL_BUFFER_SIZE"}, {GL_BUFFER_USAGE, "GL_BUFFER_USAGE"},
   };
   return GLES2Util::GetQualifiedEnumString(string_table,
                                            arraysize(string_table), value);
 }
 
 std::string GLES2Util::GetStringBufferTarget(uint32_t value) {
   static const EnumToString string_table[] = {
       {GL_ARRAY_BUFFER, "GL_ARRAY_BUFFER"},
       {GL_ELEMENT_ARRAY_BUFFER, "GL_ELEMENT_ARRAY_BUFFER"},
+      {GL_COPY_READ_BUFFER, "GL_COPY_READ_BUFFER"},
+      {GL_COPY_WRITE_BUFFER, "GL_COPY_WRITE_BUFFER"},
+      {GL_PIXEL_PACK_BUFFER, "GL_PIXEL_PACK_BUFFER"},
+      {GL_PIXEL_UNPACK_BUFFER, "GL_PIXEL_UNPACK_BUFFER"},
+      {GL_TRANSFORM_FEEDBACK_BUFFER, "GL_TRANSFORM_FEEDBACK_BUFFER"},
+      {GL_UNIFORM_BUFFER, "GL_UNIFORM_BUFFER"},
   };
   return GLES2Util::GetQualifiedEnumString(string_table,
                                            arraysize(string_table), value);
 }
 
 std::string GLES2Util::GetStringBufferUsage(uint32_t value) {
   static const EnumToString string_table[] = {
       {GL_STREAM_DRAW, "GL_STREAM_DRAW"},
       {GL_STATIC_DRAW, "GL_STATIC_DRAW"},
       {GL_DYNAMIC_DRAW, "GL_DYNAMIC_DRAW"},
@@ skipping 832 matching lines @@
 
 std::string GLES2Util::GetStringVertexPointer(uint32_t value) {
   static const EnumToString string_table[] = {
       {GL_VERTEX_ATTRIB_ARRAY_POINTER, "GL_VERTEX_ATTRIB_ARRAY_POINTER"},
   };
   return GLES2Util::GetQualifiedEnumString(string_table,
                                            arraysize(string_table), value);
 }
 
 #endif  // GPU_COMMAND_BUFFER_COMMON_GLES2_CMD_UTILS_IMPLEMENTATION_AUTOGEN_H_