Backed out changeset f488d4345f75 (bug 1676852) on request by smaug

layout/base/nsRefreshDriver.cpp

@@ -639,8 +639,6 @@ class VsyncRefreshDriverTimer : public RefreshDriverTimer {
                 NS_DispatchToCurrentThreadQueue(vsyncEvent.forget(), slowRate,
                                                 EventQueuePriority::Idle);
               }
-              // Pretend that RefreshDriver did run on time.
-              mVsyncRefreshDriverTimer->mLastFireTime = TimeStamp::Now();
               return;
             }
           }