Bug 688044 - ASSERTION: Why is the root in mDirtyRoots already? r=bzbarsky

layout/base/nsPresShell.cpp

@@ -1962,18 +1962,19 @@ PresShell::InitialReflow(nscoord aWidth, nscoord aHeight)
 
   NS_ASSERTION(rootFrame, "How did that happen?");
 
-  // Note: Because the frame just got created, it has the NS_FRAME_IS_DIRTY
-  // bit set.  Unset it so that FrameNeedsReflow() will work right.
-  NS_ASSERTION(!mDirtyRoots.Contains(rootFrame),
-               "Why is the root in mDirtyRoots already?");
-
-  rootFrame->RemoveStateBits(NS_FRAME_IS_DIRTY |
-                             NS_FRAME_HAS_DIRTY_CHILDREN);
-  FrameNeedsReflow(rootFrame, eResize, NS_FRAME_IS_DIRTY);
-
-  NS_ASSERTION(mDirtyRoots.Contains(rootFrame),
-               "Should be in mDirtyRoots now");
-  NS_ASSERTION(mReflowScheduled, "Why no reflow scheduled?");
+  // Note: when the frame was created above it had the NS_FRAME_IS_DIRTY bit
+  // set, but XBL processing could have caused a reflow which clears it.
+  if (NS_LIKELY(rootFrame->GetStateBits() & NS_FRAME_IS_DIRTY)) {
+    // Unset the DIRTY bits so that FrameNeedsReflow() will work right.
+    rootFrame->RemoveStateBits(NS_FRAME_IS_DIRTY |
+                               NS_FRAME_HAS_DIRTY_CHILDREN);
+    NS_ASSERTION(!mDirtyRoots.Contains(rootFrame),
+                 "Why is the root in mDirtyRoots already?");
+    FrameNeedsReflow(rootFrame, eResize, NS_FRAME_IS_DIRTY);
+    NS_ASSERTION(mDirtyRoots.Contains(rootFrame),
+                 "Should be in mDirtyRoots now");
+    NS_ASSERTION(mReflowScheduled, "Why no reflow scheduled?");
+  }
 
   // Restore our root scroll position now if we're getting here after EndLoad
   // got called, since this is our one chance to do it.  Note that we need not