Remove Sync GetPose VRService call, implement VRVSyncProvider

This CL removes the Synchronous GetPose call from the VRService, in favor of a VRVSyncProvider that sends the pose with each VSync.

BUG=655722
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_site_isolation

Review-Url: https://codereview.chromium.org/2624633002
Cr-Commit-Position: refs/heads/master@{#446581}
31 files changed