https://bugs.webkit.org/show_bug.cgi?id=110936

Reviewed by Brent Fulgham.

Add support for the HALF_FLOAT_OES texture format from texImage2D
and texSubImage2D.

A lot of this patch comes from the original patch on the bug
by Nayan Kumar, and the Blink commit:
https://codereview.chromium.org/13842017

Tests: fast/canvas/webgl/oes-texture-half-float-with-canvas.html
       fast/canvas/webgl/oes-texture-half-float-with-image.html
       fast/canvas/webgl/oes-texture-half-float-with-video.html

* html/canvas/OESTextureHalfFloat.idl: New HALF_FLOAT_OES constant value.
* html/canvas/WebGLRenderingContext.cpp:
(WebCore::WebGLRenderingContext::validateTexFunc): Remove the code that
would bail if half-float values were used.
* platform/graphics/GraphicsContext3D.cpp:
- Return appropriate DataFormats for half floating point types.
- Copy the float -> half-float code from Blink
- New pack functions for half floats
* platform/graphics/GraphicsContext3D.h: New format types.
* platform/graphics/opengl/GraphicsContext3DOpenGLCommon.cpp:
(WebCore::GraphicsContext3D::texSubImage2D): Use GL_HALF_FLOAT_ARB if we're passed
a HALF_FLOAT_OES.

LayoutTests: [WebGL] Support for texImage2D/texSubImage2D of type HALF_FLOAT_OES
https://bugs.webkit.org/show_bug.cgi?id=110936

Reviewed by Brent Fulgham.

New tests for half-float textures.

* fast/canvas/webgl/oes-texture-half-float-expected.txt:
* fast/canvas/webgl/oes-texture-half-float-not-supported-expected.txt: Removed.
* fast/canvas/webgl/oes-texture-half-float-not-supported.html: Removed.
* fast/canvas/webgl/oes-texture-half-float-with-canvas-expected.txt: Added.
* fast/canvas/webgl/oes-texture-half-float-with-canvas.html: Added.
* fast/canvas/webgl/oes-texture-half-float-with-image-expected.txt: Added.
* fast/canvas/webgl/oes-texture-half-float-with-image.html: Added.
* fast/canvas/webgl/oes-texture-half-float-with-video-expected.txt: Added.
* fast/canvas/webgl/oes-texture-half-float-with-video.html: Added.
* fast/canvas/webgl/oes-texture-half-float.html:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@160119 268f45cc-cd09-0410-ab3c-d52691b4dbfc