Disable sampler objects when using ES2 shading language on ES3 contexts.

Bug: https://github.com/flutter/flutter/issues/24402
Bug: https://github.com/flutter/flutter/issues/24289
Bug: https://github.com/flutter/flutter/issues/24391
Bug: https://github.com/flutter/flutter/issues/24517
Bug: https://github.com/flutter/flutter/issues/23900

Change-Id: I15aa8241f0c4d4b25f00aed9f6fabbe73ecf89ce
Reviewed-on: https://skia-review.googlesource.com/c/172405
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
1 file changed