gpu: Correct GMB format for GL_RGB BackTexture.

gpu/command_buffer/service/gles2_cmd_decoder.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.
 
 #include "gpu/command_buffer/service/gles2_cmd_decoder.h"
 
 #include <limits.h>
 #include <stddef.h>
 #include <stdint.h>
 #include <stdio.h>
@@ skipping 2758 matching lines @@
   return decoder_->should_use_native_gmb_for_backbuffer_
              ? decoder_->GetContextGroup()
                    ->image_factory()
                    ->RequiredTextureType()
              : GL_TEXTURE_2D;
 }
 
 bool BackTexture::AllocateNativeGpuMemoryBuffer(const gfx::Size& size,
                                                 GLenum format,
                                                 bool zero) {
-  gfx::BufferFormat buffer_format = gfx::BufferFormat::RGBA_8888;
+  DCHECK(format == GL_RGB || format == GL_RGBA);
   scoped_refptr<gl::GLImage> image =
       decoder_->GetContextGroup()->image_factory()->CreateAnonymousImage(
-          size, buffer_format, format);
+          size,
+          format == GL_RGB ? gfx::BufferFormat::RGBX_8888
+                           : gfx::BufferFormat::RGBA_8888,
+          format);
   if (!image || !image->BindTexImage(Target()))
     return false;
 
   image_ = image;
   decoder_->texture_manager()->SetLevelInfo(
       texture_ref_.get(), Target(), 0, image_->GetInternalFormat(),
       size.width(), size.height(), 1, 0, image_->GetInternalFormat(),
       GL_UNSIGNED_BYTE, gfx::Rect(size));
   decoder_->texture_manager()->SetLevelImage(texture_ref_.get(), Target(), 0,
                                              image_.get(), Texture::BOUND);
@@ skipping 16404 matching lines @@
 }
 
 // Include the auto-generated part of this file. We split this because it means
 // we can easily edit the non-auto generated parts right here in this file
 // instead of having to edit some template or the code generator.
 #include "base/macros.h"
 #include "gpu/command_buffer/service/gles2_cmd_decoder_autogen.h"
 
 }  // namespace gles2
 }  // namespace gpu