Centralize GL format workarounds. Instead of trying to encapsulate the GL texture format workarounds into tables, use functions that do manual checks for specific cases. Simplifies the logic. Fixes: * conformance/extensions/ext-sRGB.html * conformance/extensions/oes-texture-half-float.html * conformance/extensions/oes-texture-half-float-with-canvas.html * conformance/extensions/oes-texture-half-float-with-image.htm * conformance/extensions/oes-texture-half-float-with-video.html BUG=angleproject:884 Change-Id: Ifb719fff908680fddc7c53a544e2284a42a58356 Reviewed-on: https://chromium-review.googlesource.com/289082 Reviewed-by: Kenneth Russell <kbr@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org> Tested-by: Geoff Lang <geofflang@chromium.org>