[Texmap] Implement BGRA swizzling detection
https://bugs.webkit.org/show_bug.cgi?id=81103

For OpenGLES if the extension EXT_texture_format_BGRA8888 is supported
the internal and external formats need to be BGRA.

Reviewed by Noam Rosenthal.

* platform/graphics/texmap/TextureMapperGL.cpp:
(WebCore):
(WebCore::driverSupportsExternalTextureBGRA):
(WebCore::driverSupportsSubImage):
(WebCore::BitmapTextureGL::didReset):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@141807 268f45cc-cd09-0410-ab3c-d52691b4dbfc