[SPv175] Only check that the mapped rect is empty, not that it equals the empty rect.

Any empty rect suffices to make it correct to return the empty rect when
computing visual rects in graphics layer space.

Bug:825125

Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
Change-Id: I332183a7b31e877fef01bab91fd9e835b828b9e5
Reviewed-on: https://chromium-review.googlesource.com/987401
Commit-Queue: Tien-Ren Chen <trchen@chromium.org>
Reviewed-by: Tien-Ren Chen <trchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#547320}

third_party/WebKit/Source/platform/graphics/compositing/ChunkToLayerMapper.cpp

@@ -70,7 +70,7 @@ IntRect ChunkToLayerMapper::MapVisualRect(const FloatRect& rect) const {
     mapped_rect.Intersect(clip_rect_.Rect());
 
   if (mapped_rect.IsEmpty()) {
-    DCHECK_EQ(IntRect(), MapUsingGeometryMapper(rect));
+    DCHECK(MapUsingGeometryMapper(rect).IsEmpty());
     return IntRect();
   }