WebVR: Defer GetVSync calls until the current frame is submitted.

third_party/WebKit/Source/platform/RuntimeEnabledFeatures.json5

Index: third_party/WebKit/Source/platform/RuntimeEnabledFeatures.json5
diff --git a/third_party/WebKit/Source/platform/RuntimeEnabledFeatures.json5 b/third_party/WebKit/Source/platform/RuntimeEnabledFeatures.json5
index c45bf01d223b8bfbf4184dd2d14efde268885df8..29f9580d5488f230be2db8c2ea8a57e554eb9d04 100644
--- a/third_party/WebKit/Source/platform/RuntimeEnabledFeatures.json5
+++ b/third_party/WebKit/Source/platform/RuntimeEnabledFeatures.json5
@@ -1067,7 +1067,9 @@
       name: "WebVRExperimentalRendering",
       // Don't mark this as depends_on: ["WebVR"], we want to be able to turn
       // it on for just origin trial sites where the dependency is unset.
-      status: "experimental",
+      // We also need it for tests since the default mode requires re-entrant
+      // mojo event handling, and the Javascript mocks don't support that.
+      status: "test",
     },
     {
       name: "WebVTTRegions",