Add fPreferExternalImagesOverES3 to GrContextOptions

This forces us to use the ES2 shading language when we have an ES3
context, but the driver claims to only support GL_OES_EGL_image_external
(and not the _essl3 variant). Many of these devices will work correctly
if we blindly enable both extensions, but there are some that won't.

Bug: skia:
Change-Id: Id632003a1905ea61b46166befd30905a57cead69
Reviewed-on: https://skia-review.googlesource.com/126681
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
2 files changed