Implement EXT_draw_buffers WebGL extention support in command buffer.

gpu/command_buffer/common/gles2_cmd_ids_autogen.h

 // Copyright (c) 2012 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
 // DO NOT EDIT!
 
 #ifndef GPU_COMMAND_BUFFER_COMMON_GLES2_CMD_IDS_AUTOGEN_H_
 #define GPU_COMMAND_BUFFER_COMMON_GLES2_CMD_IDS_AUTOGEN_H_
@@ skipping 232 matching lines @@
   OP(ReleaseTexImage2DCHROMIUM)                                /* 486 */ \
   OP(TraceBeginCHROMIUM)                                       /* 487 */ \
   OP(TraceEndCHROMIUM)                                         /* 488 */ \
   OP(AsyncTexSubImage2DCHROMIUM)                               /* 489 */ \
   OP(AsyncTexImage2DCHROMIUM)                                  /* 490 */ \
   OP(WaitAsyncTexImage2DCHROMIUM)                              /* 491 */ \
   OP(DiscardFramebufferEXT)                                    /* 492 */ \
   OP(DiscardFramebufferEXTImmediate)                           /* 493 */ \
   OP(LoseContextCHROMIUM)                                      /* 494 */ \
   OP(WaitSyncPointCHROMIUM)                                    /* 495 */ \
+  OP(DrawBuffersEXT)                                           /* 496 */ \
+  OP(DrawBuffersEXTImmediate)                                  /* 497 */ \
 
 enum CommandId {
   kStartPoint = cmd::kLastCommonId,  // All GLES2 commands start after this.
 #define GLES2_CMD_OP(name) k ## name,
   GLES2_COMMAND_LIST(GLES2_CMD_OP)
 #undef GLES2_CMD_OP
   kNumCommands
 };
 
 #endif  // GPU_COMMAND_BUFFER_COMMON_GLES2_CMD_IDS_AUTOGEN_H_