[PE] Optimize InvalidatePaintUsingContainer.

If a paint invalidation container returns true from IsPaintInvalidationContainer(),
that means it is composited, which in turn must mean the containing LayoutView is composited.

This allows us to simplify the code and avoid a call to View(), which may be expensive
because it has to first dereference the document.

Bug: 814251
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
Change-Id: I79cc37ee79271c2030a9f5c832ba5640ca8445c9
Reviewed-on: https://chromium-review.googlesource.com/957962Reviewed-by: Philip Rogers <pdr@chromium.org>
Commit-Queue: Chris Harrelson <chrishtr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#542333}

third_party/WebKit/Source/core/paint/ObjectPaintInvalidator.cpp

@@ -360,14 +360,9 @@ void ObjectPaintInvalidator::InvalidatePaintUsingContainer(
   if (!paint_invalidation_container.IsPaintInvalidationContainer()) {
     InvalidatePaintRectangleOnWindow(paint_invalidation_container,
                                      EnclosingIntRect(dirty_rect));
-  }
-
-  auto* view = paint_invalidation_container.View();
-  if (view && view->UsesCompositing()) {
-    if (paint_invalidation_container.IsPaintInvalidationContainer()) {
-      SetBackingNeedsPaintInvalidationInRect(paint_invalidation_container,
-                                             dirty_rect, invalidation_reason);
-    }
+  } else {
+    SetBackingNeedsPaintInvalidationInRect(paint_invalidation_container,
+                                           dirty_rect, invalidation_reason);
   }
 }