Implement EXT_draw_buffers WebGL extention support in command buffer.

gpu/command_buffer/common/gles2_cmd_utils.cc

 // 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 here so other GLES2 related files can have a common set of
 // includes where appropriate.
 
 #include <stdio.h>
 #include <GLES2/gl2.h>
 #include <GLES2/gl2ext.h>
@@ skipping 604 matching lines @@
     case GL_STENCIL_INDEX8:
       return kStencil;
     case GL_DEPTH_STENCIL_OES:
     case GL_DEPTH24_STENCIL8_OES:
       return kDepth | kStencil;
     default:
       return 0x0000;
   }
 }
 
-uint32 GLES2Util::GetChannelsNeededForAttachmentType(int type) {
+uint32 GLES2Util::GetChannelsNeededForAttachmentType(
+    int type, uint32 max_color_attachments) {
   switch (type) {
-    case GL_COLOR_ATTACHMENT0:
-      return kRGBA;
     case GL_DEPTH_ATTACHMENT:
       return kDepth;
     case GL_STENCIL_ATTACHMENT:
       return kStencil;
     default:
+      if (type >= GL_COLOR_ATTACHMENT0 &&
+          type < static_cast<int>(
+              GL_COLOR_ATTACHMENT0 + max_color_attachments)) {
+        return kRGBA;
+      }
       return 0x0000;
   }
 }
 
 std::string GLES2Util::GetStringEnum(uint32 value) {
   const EnumToString* entry = enum_to_string_table_;
   const EnumToString* end = entry + enum_to_string_table_len_;
   for (;entry < end; ++entry) {
     if (value == entry->value) {
       return entry->name;
@@ skipping 148 matching lines @@
   }
 
   return true;
 }
 
 #include "../common/gles2_cmd_utils_implementation_autogen.h"
 
 }  // namespace gles2
 }  // namespace gpu