When GL_RGBA readPixels are slow do swizzle using a draw then readPixels with GL_BGRA

[bsalomon, 2011-11-08 15:59:08]

ANGLE is horribly slow if we call glReadPixels with GL_RGBA. With this change
swap R and B using the shader, then do the readPixels with GL_BGRA which is
ANGLE's fast path.

[TomH, 2011-11-08 19:08:12]

LGTM

http://codereview.appspot.com/5339051/diff/2001/src/gpu/GrContext.cpp
File src/gpu/GrContext.cpp (left):

http://codereview.appspot.com/5339051/diff/2001/src/gpu/GrContext.cpp#oldcode59
src/gpu/GrContext.cpp:59: return GrContext::Create(kOpenGL_Shaders_GrEngine, 0);
What happened to this?

[bsalomon, 2011-11-08 19:18:47]

On 2011/11/08 19:08:12, TomH wrote:
> LGTM
> 
> http://codereview.appspot.com/5339051/diff/2001/src/gpu/GrContext.cpp
> File src/gpu/GrContext.cpp (left):
> 
>
http://codereview.appspot.com/5339051/diff/2001/src/gpu/GrContext.cpp#oldcode59
> src/gpu/GrContext.cpp:59: return GrContext::Create(kOpenGL_Shaders_GrEngine,
0);
> What happened to this?

I have been meaning to remove it for a while. It was relevant to this change at
one moment in time, but now it's not. I'll revert that portion of the change
before committing.