Bug 1442063 - Don't call FlushRendering() after we reached the state of STATE_WAITING_TO_FINISH. r=dbaron

Once we reached the state of STATE_WAITING_TO_FINISH, we just need to wait for
the final MozAfterPaint which is corresponding to flushRendering() after
"reftest-wait" removal.

MozReview-Commit-ID: EJxDYUnqbmr

--HG--
extra : rebase_source : fdb5c30142def4c0138bc6af2c510d85f30ed7f3

layout/tools/reftest/reftest-content.js

@@ -582,7 +582,11 @@ function WaitForTestEnd(contentRootElement, inPrintMode, spellCheckedElements) {
             return;
         }
 
-        FlushRendering();
+        // We don't need to flush styles any more when we are in the state
+        // after reftest-wait has removed.
+        if (state != STATE_WAITING_TO_FINISH) {
+          FlushRendering();
+        }
 
         switch (state) {
         case STATE_WAITING_TO_FIRE_INVALIDATE_EVENT: {