Bug 1165458. Raise vsync timeout limit for gtests. r=kats

gfx/tests/gtest/TestVsync.cpp

@@ -22,7 +22,8 @@ using namespace mozilla::layers;
 using ::testing::_;
 
 // Timeout for vsync events to occur in milliseconds
-const int kVsyncTimeoutMS = 50;
+// Windows 8.1 has intermittents at 50 ms. Raise limit to 5 vsync intervals.
+const int kVsyncTimeoutMS = 80;
 
 class TestVsyncObserver : public VsyncObserver {
 public: