This removes the check for robust resource init from prepareForDraw.
It should improve performance more when WebGL compatiblity is enabled.
Also inlines Context::syncDirtyBits and Context::prepareForDraw.

Reduces CPU overhead in all draw and dispatch calls up to 5%.

Bug: angleproject:2966
Change-Id: I7e9009a501c0331a6140bc78678aef27e38c3df2
Reviewed-on: https://chromium-review.googlesource.com/c/1347453Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>