Perform glReadPixels with PBOs in the gpu, if PBOs are available.

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 <set>
 #include <string>
 #include "base/containers/hash_tables.h"
@@ skipping 27 matching lines @@
     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 enable_shader_name_hashing;
     bool enable_samplers;
     bool ext_draw_buffers;
     bool ext_frag_depth;
+    bool use_async_readpixels;
   };
 
   struct Workarounds {
     Workarounds();
 
 #define GPU_OP(type, name) bool name;
     GPU_DRIVER_BUG_WORKAROUNDS(GPU_OP)
 #undef GPU_OP
 
     // Note: 0 here means use driver limit.
@@ skipping 57 matching lines @@
   // Flags for Workarounds.
   Workarounds workarounds_;
 
   DISALLOW_COPY_AND_ASSIGN(FeatureInfo);
 };
 
 }  // namespace gles2
 }  // namespace gpu
 
 #endif  // GPU_COMMAND_BUFFER_SERVICE_FEATURE_INFO_H_