Fix flattening for scrollable areas.

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 "config.h"
 #include "core/layout/compositing/CompositedLayerMapping.h"
 
 #include "core/frame/FrameView.h"
 #include "core/html/HTMLIFrameElement.h"
 #include "core/layout/LayoutBoxModelObject.h"
@@ skipping 16 matching lines @@
     IntRect recomputeInterestRect(const GraphicsLayer* graphicsLayer)
     {
         return static_cast<CompositedLayerMapping*>(graphicsLayer->client())->recomputeInterestRect(graphicsLayer);
     }
 
     IntRect computeInterestRect(const CompositedLayerMapping* compositedLayerMapping, GraphicsLayer* graphicsLayer, IntRect previousInterestRect)
     {
         return compositedLayerMapping->computeInterestRect(graphicsLayer, previousInterestRect);
     }
 
+    bool shouldFlattenTransform(const GraphicsLayer& layer) const
+    {
+        return layer.shouldFlattenTransform();
+    }
+
     bool interestRectChangedEnoughToRepaint(const IntRect& previousInterestRect, const IntRect& newInterestRect, const IntSize& layerSize)
     {
         return CompositedLayerMapping::interestRectChangedEnoughToRepaint(previousInterestRect, newInterestRect, layerSize);
     }
 
     IntRect previousInterestRect(const GraphicsLayer* graphicsLayer)
     {
         return graphicsLayer->m_previousInterestRect;
     }
 
@@ skipping 210 matching lines @@
     document().view()->updateAllLifecyclePhases();
     EXPECT_TRUE(graphicsLayer->maskLayer());
     EXPECT_FALSE(graphicsLayer->contentsClippingMaskLayer());
 
     videoElement->setAttribute(HTMLNames::styleAttr, styleWithoutClipping);
     document().view()->updateAllLifecyclePhases();
     EXPECT_FALSE(graphicsLayer->maskLayer());
     EXPECT_FALSE(graphicsLayer->contentsClippingMaskLayer());
 }
 
+TEST_F(CompositedLayerMappingTest, ScrollContentsFlattenForScroller)
+{
+    setBodyInnerHTML(
+        "<style>div::-webkit-scrollbar{ width: 5px; }</style>"
+        "<div id='scroller' style='width: 100px; height: 100px; overflow: scroll; will-change: transform'>"
+        "<div style='width: 1000px; height: 1000px;'>Foo</div>Foo</div>");
+
+    document().view()->updateAllLifecyclePhases();
+    Element* element = document().getElementById("scroller");
+    PaintLayer* paintLayer = toLayoutBoxModelObject(element->layoutObject())->layer();
+    CompositedLayerMapping* compositedLayerMapping = paintLayer->compositedLayerMapping();
+
+    ASSERT_TRUE(compositedLayerMapping);
+
+    EXPECT_FALSE(shouldFlattenTransform(*compositedLayerMapping->mainGraphicsLayer()));
+    EXPECT_FALSE(shouldFlattenTransform(*compositedLayerMapping->scrollingLayer()));
+    EXPECT_TRUE(shouldFlattenTransform(*compositedLayerMapping->scrollingContentsLayer()));
+}
+
 TEST_F(CompositedLayerMappingTest, InterestRectChangedEnoughToRepaintEmpty)
 {
     IntSize layerSize(1000, 1000);
     // Both empty means there is nothing to do.
     EXPECT_FALSE(interestRectChangedEnoughToRepaint(IntRect(), IntRect(), layerSize));
     // Going from empty to non-empty means we must re-record because it could be the first frame after construction or Clear.
     EXPECT_TRUE(interestRectChangedEnoughToRepaint(IntRect(), IntRect(0, 0, 1, 1), layerSize));
     // Going from non-empty to empty is not special-cased.
     EXPECT_FALSE(interestRectChangedEnoughToRepaint(IntRect(0, 0, 1, 1), IntRect(), layerSize));
 }
@@ skipping 241 matching lines @@
     ASSERT_TRUE(target);
 
     EXPECT_RECT_EQ(IntRect(0, 0, 200, 200), recomputeInterestRect(target->layoutObject()->enclosingLayer()->graphicsLayerBacking()));
 
     subframe->detach(FrameDetachType::Remove);
     static_cast<SingleChildFrameLoaderClient*>(document().frame()->client())->setChild(nullptr);
     document().frame()->host()->decrementSubframeCount();
 }
 
 } // namespace blink