* Expose GL_CHROMIUM_color_buffer_float_rgb and
   GL_CHROMIUM_color_buffer_float_rgba
 * Fix many texture formats that were incorrectly checking the wrong
   extension for support or renderability.
 * Make all floating point texture extensions dynamically enableable.

BUG=angleproject:1958
BUG=angleproject:1715

Change-Id: Iefccc8b5ae5edd97623affa9de05b1d9af5c9598
Reviewed-on: https://chromium-review.googlesource.com/468450Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Geoff Lang <geofflang@chromium.org>