Implement EXT_draw_buffers WebGL extention support in command buffer.

gpu/command_buffer/service/feature_info.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.
 
 #ifndef GPU_COMMAND_BUFFER_SERVICE_FEATURE_INFO_H_
 #define GPU_COMMAND_BUFFER_SERVICE_FEATURE_INFO_H_
 
 #include <string>
 #include "base/hash_tables.h"
 #include "base/memory/ref_counted.h"
@@ skipping 21 matching lines @@
     bool angle_translated_shader_source;
     bool angle_pack_reverse_row_order;
     bool arb_texture_rectangle;
     bool angle_instanced_arrays;
     bool occlusion_query_boolean;
     bool use_arb_occlusion_query2_for_occlusion_query_boolean;
     bool use_arb_occlusion_query_for_occlusion_query_boolean;
     bool native_vertex_array_object;
     bool disable_workarounds;
     bool enable_shader_name_hashing;
+    bool ext_draw_buffers;
   };
 
   struct Workarounds {
     Workarounds();
 
     bool clear_alpha_in_readpixels;
     bool clear_uniforms_before_program_use;
     bool needs_glsl_built_in_function_emulation;
     bool needs_offscreen_buffer_workaround;
     bool reverse_point_sprite_coord_origin;
@@ skipping 63 matching lines @@
   // Flags for Workarounds.
   Workarounds workarounds_;
 
   DISALLOW_COPY_AND_ASSIGN(FeatureInfo);
 };
 
 }  // namespace gles2
 }  // namespace gpu
 
 #endif  // GPU_COMMAND_BUFFER_SERVICE_FEATURE_INFO_H_