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

gpu/command_buffer/common/gles2_cmd_utils_implementation_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_UTILS_IMPLEMENTATION_AUTOGEN_H_
 #define GPU_COMMAND_BUFFER_COMMON_GLES2_CMD_UTILS_IMPLEMENTATION_AUTOGEN_H_
@@ skipping 68 matching lines @@
   { 0x8B5C, "GL_FLOAT_MAT4", },
   { 0x8B5B, "GL_FLOAT_MAT3", },
   { 0x8B5A, "GL_FLOAT_MAT2", },
   { 0x0D05, "GL_PACK_ALIGNMENT", },
   { 0x87FF, "GL_PROGRAM_BINARY_FORMATS_OES", },
   { 0x87FE, "GL_NUM_PROGRAM_BINARY_FORMATS_OES", },
   { 0x2600, "GL_NEAREST", },
   { 0x2601, "GL_LINEAR", },
   { 0x8C03, "GL_COMPRESSED_RGBA_PVRTC_2BPPV1_IMG", },
   { 0x9242, "GL_UNPACK_UNPREMULTIPLY_ALPHA_CHROMIUM", },
+  { 0x88BA, "GL_READ_WRITE", },
   { 0x88BB, "GL_BUFFER_ACCESS_OES", },
   { 0x88BC, "GL_BUFFER_MAPPED_OES", },
   { 0x88BD, "GL_BUFFER_MAP_POINTER_OES", },
   { 0x0C10, "GL_SCISSOR_BOX", },
   { 0x0C11, "GL_SCISSOR_TEST", },
   { 0x80000000, "GL_MULTISAMPLE_BUFFER_BIT7_QCOM", },
   { 0x300E, "GL_CONTEXT_LOST", },
   { 0x02000000, "GL_MULTISAMPLE_BUFFER_BIT1_QCOM", },
   { 0x8C2F, "GL_ANY_SAMPLES_PASSED_EXT", },
   { 0x8BD2, "GL_TEXTURE_WIDTH_QCOM", },
@@ skipping 1297 matching lines @@
 std::string GLES2Util::GetStringVertexPointer(uint32 value) {
   static 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_