Re-enable QCOM_tiled_rendering, but check for gl functions

This enables tiled rendering when the extension is
reported AND the "optional" start and end tiling
gl functions were found.

Hopefully this will correct the hard crashes on the
Pixel 2XL waterfall bots, while still properly disabling
tiled rendering for the devices found in the Flutter bugs:

Bug: flutter:47164, flutter:47804
Change-Id: Ia96a89053305378d434304b7b4fbc0f5e49cd97e
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/264695
Reviewed-by: Brian Salomon <bsalomon@google.com>
Reviewed-by: Chris Dalton <csmartdalton@google.com>
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
2 files changed