The extension behavior was being shared between translation units,
this was causing states to be cached between shader compilers. This
has been fixed now by adding a new ResetExtensionBehavior() function.

A unit test has also been added for testing extensions when compiling
shaders. A test has been included which tests that the internal state
of the extension behavior is being reset properly.

BUG=453543
Change-Id: Icb2a07019b5db972dc75cdbbdece4b7e9757c682
Reviewed-on: https://chromium-review.googlesource.com/245522Tested-by: David Yen <dyen@chromium.org>
Reviewed-by: Zhenyao Mo <zmo@chromium.org>