Add GPU workaround for eglClientWaitSyncKHR timeout on S8

Samsung's implementation of the Adreno 540 driver on Android N as used
on the S8/S8+ has a bug where eglClientWaitSyncKHR with a nonzero
timeout waits much longer than the specified timeout. This is fixed
in the Android O update for these devices.

Workaround is to replace the timeout with polling for completion.
Since we don't know if we need the workaround until the GPU process
initialization completes, add a OnGpuConnectionReady callback
in VrShellGl to check for this.

This bug is specific to Samsung S8/S8+ on Android N, but there isn't
currently a way to restrict the filter to those devices. The
functionality is currently only used for WebVR on Daydream ready
devices, and the non-Samsung Daydream devices generally use Android O,
so an overbroad match seems acceptable.

BUG=760389

Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Change-Id: I72b92d529307fe114d850eea576fd41fe0fcb645
Reviewed-on: https://chromium-review.googlesource.com/939724


Reviewed-by: Antoine Labour <piman@chromium.org>
Reviewed-by: Brandon Jones <bajones@chromium.org>
Commit-Queue: Klaus Weidner <klausw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#539601}