Bug 969591 - Cleanup Thebes Layer if mRegionToDraw is Empty and we still have a buffer allocated. r=mattwoodrow

gfx/layers/RotatedBuffer.cpp

@@ -503,8 +503,16 @@ RotatedContentBuffer::BeginPaint(ThebesLayer* aLayer,
   // or call CreateBuffer before this call.
   FinalizeFrame(result.mRegionToDraw);
 
-  if (result.mRegionToDraw.IsEmpty())
+  // Have some cases where the region to draw is empty,
+  // but the needed region is not empty, so we still need to allocate
+  // a clean buffer for those cases. If everything is empty, then clear out
+  // the buffers.
+  if (result.mRegionToDraw.IsEmpty() && canReuseBuffer) {
+    if (neededRegion.IsEmpty()) {
+      Clear();
+    }
     return result;
+  }
 
   nsIntRect drawBounds = result.mRegionToDraw.GetBounds();
   RefPtr<DrawTarget> destDTBuffer;