Reland "Only promote opaque scrollers which are stacking contexts."

third_party/WebKit/Source/core/layout/compositing/CompositedLayerMappingTest.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/layout/compositing/CompositedLayerMapping.h"
 
 #include "core/frame/FrameView.h"
 #include "core/layout/LayoutBoxModelObject.h"
 #include "core/layout/LayoutTestHelper.h"
 #include "core/layout/api/LayoutViewItem.h"
@@ skipping 856 matching lines @@
   mapping = paintLayer->compositedLayerMapping();
   EXPECT_FALSE(paintLayer->needsCompositedScrolling());
   EXPECT_FALSE(mapping->decorationOutlineLayer());
 }
 
 TEST_P(CompositedLayerMappingTest,
        DecorationOutlineLayerCreatedAndDestroyedInCompositedScrolling) {
   setBodyInnerHTML(
       "<style>"
       "#scroller { overflow: scroll; height: 200px; width: 200px; background: "
-      "white local content-box; outline: 1px solid blue;}"
+      "white local content-box; outline: 1px solid blue; contain: paint; }"
       "#scrolled { height: 300px; }"
       "</style>"
       "<div id=\"parent\">"
       "  <div id=\"scroller\"><div id=\"scrolled\"></div></div>"
       "</div>");
   document().view()->updateAllLifecyclePhases();
 
   Element* scroller = document().getElementById("scroller");
   PaintLayer* paintLayer =
       toLayoutBoxModelObject(scroller->layoutObject())->layer();
@@ skipping 189 matching lines @@
     document().view()->updateAllLifecyclePhases();
     ASSERT_EQ(document().documentElement(),
               rootScrollerController.globalRootScroller());
 
     EXPECT_TRUE(mapping3->clippingLayer());
     EXPECT_TRUE(mapping3->clippingLayer()->platformLayer()->masksToBounds());
   }
 }
 
 }  // namespace blink