Code:  void VRDisplay::FocusChanged() {
   vr_v_sync_provider_.reset();
   ConnectVSyncProvider();
 }

Vulnerability Type: DoS 
CWE ID: 
Summary: Multiple unspecified vulnerabilities in Google Chrome before 43.0.2357.65 allow attackers to cause a denial of service or possibly have other impact via unknown vectors.
Commit Message: WebVR: fix initial vsync

Applications sometimes use window.rAF while not presenting, then switch to
vrDisplay.rAF after presentation starts. Depending on the animation loop's
timing, this can cause a race condition where presentation has been started
but there's no vrDisplay.rAF pending yet. Ensure there's at least vsync
being processed after presentation starts so that a queued window.rAF
can run and schedule a vrDisplay.rAF.

BUG=711789

Review-Url: https://codereview.chromium.org/2848483003
Cr-Commit-Position: refs/heads/master@{#468167}