Improve indexed gl state related GL commands.

gpu/command_buffer/service/gles2_cmd_validation_autogen.h

 // Copyright 2014 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
 // It's formatted by clang-format using chromium coding style:
 //    clang-format -i -style=chromium filename
 // DO NOT EDIT!
 
@@ skipping 235 matching lines @@
   bool IsValid(const GLenum value) const;
 };
 QueryObjectParameterValidator query_object_parameter;
 
 class QueryTargetValidator {
  public:
   bool IsValid(const GLenum value) const;
 };
 QueryTargetValidator query_target;
 
-class ReadBufferValidator {
- public:
-  bool IsValid(const GLenum value) const;
-};
-ReadBufferValidator read_buffer;
-
+ValueValidator<GLenum> read_buffer;
 ValueValidator<GLenum> read_pixel_format;
 ValueValidator<GLenum> read_pixel_type;
 ValueValidator<GLenum> render_buffer_format;
 ValueValidator<GLenum> render_buffer_parameter;
 ValueValidator<GLenum> render_buffer_target;
 class ResetStatusValidator {
  public:
   bool IsValid(const GLenum value) const;
 };
 ResetStatusValidator reset_status;
@@ skipping 120 matching lines @@
  public:
   bool IsValid(const GLenum value) const;
 };
 VertexAttribITypeValidator vertex_attrib_i_type;
 
 ValueValidator<GLenum> vertex_attrib_type;
 ValueValidator<GLenum> vertex_attribute;
 ValueValidator<GLenum> vertex_pointer;
 
 #endif  // GPU_COMMAND_BUFFER_SERVICE_GLES2_CMD_VALIDATION_AUTOGEN_H_