Bug 1500805 Part 2 - Ensure non-main threads are idle when diverging from the recording, r=mccr8.

--HG--
extra : rebase_source : 0d9e1ae7f0bcda2631781cc4b4a73cee88e886c8

toolkit/recordreplay/ProcessRewind.cpp

@@ -199,6 +199,11 @@ DivergeFromRecording()
     // Reset middleman call state whenever we first diverge from the recording.
     child::SendResetMiddlemanCalls();
 
+    // Make sure all non-main threads are idle before we begin diverging. This
+    // thread's new behavior can change values used by other threads and induce
+    // recording mismatches.
+    Thread::WaitForIdleThreads();
+
     thread->DivergeFromRecording();
   }
 

toolkit/recordreplay/ipc/ChildIPC.cpp

@@ -577,22 +577,21 @@ Repaint(size_t* aWidth, size_t* aHeight)
   // and the last graphics we sent will still be correct.
   Thread* compositorThread = Thread::GetById(gCompositorThreadId);
   if (!compositorThread->WillDivergeFromRecordingSoon()) {
+    // Allow the compositor to diverge from the recording so it can perform
+    // any paint we are about to trigger, or finish any in flight paint that
+    // that existed at the point we are paused at.
+    Thread::GetById(gCompositorThreadId)->SetShouldDivergeFromRecording();
+    Thread::ResumeSingleIdleThread(gCompositorThreadId);
+
     // Create an artifical vsync to see if graphics have changed since the last
     // paint and a new paint is needed.
     NotifyVsyncObserver();
 
-    if (gNumPendingPaints) {
-      // Allow the compositor to diverge from the recording so it can perform
-      // any paint we just triggered, or finish any in flight paint that that
-      // existed at the point we are paused at.
-      Thread::GetById(gCompositorThreadId)->SetShouldDivergeFromRecording();
-
-      // Wait for the compositor to finish all in flight paints, including any
-      // one we just triggered.
-      MonitorAutoLock lock(*gMonitor);
-      while (gNumPendingPaints) {
-        gMonitor->Wait();
-      }
+    // Wait for the compositor to finish all in flight paints, including any
+    // one we just triggered.
+    MonitorAutoLock lock(*gMonitor);
+    while (gNumPendingPaints) {
+      gMonitor->Wait();
     }
   }