- Supporting windowless_frame_rate; improving support without the disable-gpu-vsync flag
  - Using a staging texture when not utilizing keyed mutex with the shared texture
  - Ignore windowless_frame_rate and add default argument values for SendExternalBeginFrame.  Also, disabled keyed mutex by default
  - Updated for Chromium 68

Known issues:
- Windows now requires VS 2017 15.7.1 with 10.0.17134.0 SDK.

Known issues:
- Surface synchronization is now enabled for OSR, see issue #2447.
- Jumbo build is broken, fixed in https://crrev.com/868717ce.

Known issues:
- Download fails with empty cache path due to https://crrev.com/950748a25f.
  Fixed in https://crrev.com/087ef223ac.

Support less error-prone update of just CEF changes with automate-git.py --force-cef-update (issue #2435)

Use absolute path to avoid execution failure with automate-git.py --test-prefix=xvfb-run (issue #2435).

Support analysis of Chromium update status with automate-git.py --log-chromium-changes (issue #2435)

Linux: Fix ASAN link error: odr-violation: global 'typeinfo name for std::exception' (see https://crbug.com/832808)