Update GL_IMPLEMENTATION_COLOR_READ_FORMAT for BGRA

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 5096 matching lines @@
         // internal implementation.
         if (params) {
           if (context_->HasExtension("GL_OES_read_format")) {
             ScopedGLErrorSuppressor suppressor("GLES2DecoderImpl::GetHelper",
                                                GetErrorState());
             glGetIntegerv(pname, params);
             if (glGetError() == GL_NO_ERROR)
               return true;
           }
           *params = GLES2Util::GetGLReadPixelsImplementationFormat(
-              GetBoundReadFrameBufferInternalFormat());
+              GetBoundReadFrameBufferInternalFormat(),
+              GetBoundReadFrameBufferTextureType(),
+              feature_info_->feature_flags().ext_read_format_bgra);

[no sievers, 2016/03/08 00:26:28]

Don't we strictly speaking also have to check whether we support GL_EXT_bgra?

Sure we don't want to be noncompliant wrt the client by returning BGRA here
without having advertised GL_EXT_read_format_bgra, but isn't it a bit fragile
and relying on this being implied here (because we are in a desktop-only path
here and because of the logic in feature_info.cc).

[no sievers, 2016/03/08 00:28:44]

And also note that checking the internal format is not good enough because you
can have GL_EXT_texture_format_BGRA8888 but not support the same host memory
format.

[piman, 2016/03/08 00:48:07]

On desktop GL, the format/type is orthogonal to the internal format in the sense
that you can mix & match BGRA vs RGBA, and the driver is responsible for the
translation (for both read and write). We only get here if we support full
GL_EXT_bgra, I think?

         }
         return true;
       case GL_IMPLEMENTATION_COLOR_READ_TYPE:
         *num_written = 1;
         if (params) {
           if (context_->HasExtension("GL_OES_read_format")) {
             ScopedGLErrorSuppressor suppressor("GLES2DecoderImpl::GetHelper",
                                                GetErrorState());
             glGetIntegerv(pname, params);
             if (glGetError() == GL_NO_ERROR)
@@ skipping 10822 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