Add ANGLE_color_buffer_float and EXT_color_buffer_half_float extension support in ANGLE

Add ANGLE_color_buffer_float and EXT_color_buffer_half_float extension support in ANGLE

BUG=chromium:258371

[jun.a.jiang, 2013-07-14 05:11:48]

Thanks for Shannon's help and I can upload patch for review now although I had
met network connection issue for several times.

The basic idea of this patch is to add RGBA16F_EXT, RGB16F_EXT, RGBA32F_EXT and
RGB32F_EXT as color formats to be rendered. Meanwhile, it extends the possible
parameters of glReadPixels() and GetFramebufferAttachmentParameterriv().  

The related spec is at
http://www.khronos.org/registry/webgl/extensions/EXT_color_buffer_half_float/
and http://www.khronos.org/registry/webgl/extensions/WEBGL_color_buffer_float/.
The test cases to address these two extensions are attached for review at
https://codereview.chromium.org/18246005/.

[kbr1, 2013-07-15 20:25:27]

https://codereview.appspot.com/11238044/diff/13001/extensions/ANGLE_color_buf...
File extensions/ANGLE_color_buffer_float.txt (right):

https://codereview.appspot.com/11238044/diff/13001/extensions/ANGLE_color_buf...
extensions/ANGLE_color_buffer_float.txt:11: Kenneth Russell, Google
Jun, I think you should add yourself rather than me as the contributor here.

[kbr1, 2013-07-15 20:26:11]

+jbauman as FYI and in case he can help with the review

[jun.a.jiang, 2013-07-16 01:39:36]

On 2013/07/15 20:25:27, kbr1 wrote:
>
https://codereview.appspot.com/11238044/diff/13001/extensions/ANGLE_color_buf...
> File extensions/ANGLE_color_buffer_float.txt (right):
> 
>
https://codereview.appspot.com/11238044/diff/13001/extensions/ANGLE_color_buf...
> extensions/ANGLE_color_buffer_float.txt:11: Kenneth Russell, Google
> Jun, I think you should add yourself rather than me as the contributor here.

Hi, Kenneth. Thanks for your comments. It seems I missed my name there. I meant
to add all people that contributes to the idea and its implementation to the
contributor list. I should ask for confirmation first.
jbauman, could you help to take a look on this patch? Thanks for your help in
advance.

[kbr1, 2013-07-19 22:57:27]

Per offline discussion, the plan is to not add these extensions to ANGLE right
now, but instead to wait until the ES 3.0 branch is ready for external
contributions, and implement them against that branch.

[jun.a.jiang, 2013-07-22 02:57:19]

On 2013/07/19 22:57:27, kbr1 wrote:
> Per offline discussion, the plan is to not add these extensions to ANGLE right
> now, but instead to wait until the ES 3.0 branch is ready for external
> contributions, and implement them against that branch.

Yes, it seems better to add these extensions at a latter time. As I mentioned in
https://codereview.chromium.org/18246005/ before, rendering to FP32 textures
works well for DX9 only. When forcing to use ANGLE DX11, it seems only R32_FLOAT
and R32G32_FLOAT are renderable on Intel Graphics Cards(HD4000) on win7. In the
efforts of transition to use DX11 for ANGLE recently, there may be some more
work to be finished to support rendering to FP32 textures.
When the time comes for these extension, I'd like to pick up this issue again or
help to do some work on the compatibility issue with Intel Graphics Cards.
Meanwhile, I am open that some committers in ANGLE can help to refine this code
and land it into ANGLE directly.