Record non-stacking-context as main thread scrolling reasons

third_party/WebKit/Source/web/tests/ScrollingCoordinatorTest.cpp

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
  *     notice, this list of conditions and the following disclaimer in the
@@ skipping 1034 matching lines @@
         web_scroll_layer->MainThreadScrollingReasons() &
         MainThreadScrollingReason::kHasNonLayerViewportConstrainedObjects);
   }
 }
 
 class NonCompositedMainThreadScrollingReasonTest
     : public ScrollingCoordinatorTest {
   static const uint32_t kLCDTextRelatedReasons =
       MainThreadScrollingReason::kHasOpacityAndLCDText |
       MainThreadScrollingReason::kHasTransformAndLCDText |
-      MainThreadScrollingReason::kBackgroundNotOpaqueInRectAndLCDText;
+      MainThreadScrollingReason::kBackgroundNotOpaqueInRectAndLCDText |
+      MainThreadScrollingReason::kIsNotStackingContextAndLCDText;
 
  protected:
   NonCompositedMainThreadScrollingReasonTest() {
     RegisterMockedHttpURLLoad("two_scrollable_area.html");
     NavigateTo(base_url_ + "two_scrollable_area.html");
   }
   void TestNonCompositedReasons(const std::string& target,
                                 const uint32_t reason) {
     GetWebViewImpl()->GetSettings()->SetPreferCompositingToLCDTextEnabled(
         false);
@@ skipping 134 matching lines @@
   TestNonCompositedReasons("transparent border-radius",
                            MainThreadScrollingReason::kHasOpacityAndLCDText |
                                MainThreadScrollingReason::kHasBorderRadius);
 }
 
 TEST_P(NonCompositedMainThreadScrollingReasonTest, BoxShadowTest) {
   TestNonCompositedReasons(
       "box-shadow", MainThreadScrollingReason::kHasBoxShadowFromNonRootLayer);
 }
 
+TEST_P(NonCompositedMainThreadScrollingReasonTest, StackingContextTest) {
+  GetWebViewImpl()->GetSettings()->SetPreferCompositingToLCDTextEnabled(false);
+
+  Document* document = GetFrame()->GetDocument();
+  Element* container = document->getElementById("scroller1");
+  ASSERT_TRUE(container);
+
+  ForceFullCompositingUpdate();
+
+  // If a scroller contains all its children, it's not a stacking context.
+  PaintLayerScrollableArea* scrollable_area =
+      ToLayoutBoxModelObject(container->GetLayoutObject())->GetScrollableArea();
+  ASSERT_TRUE(scrollable_area);
+  EXPECT_TRUE(scrollable_area->GetNonCompositedMainThreadScrollingReasons() &
+              MainThreadScrollingReason::kIsNotStackingContextAndLCDText);
+
+  GetWebViewImpl()->GetSettings()->SetPreferCompositingToLCDTextEnabled(true);
+  ForceFullCompositingUpdate();
+  EXPECT_FALSE(scrollable_area->GetNonCompositedMainThreadScrollingReasons() &
+               MainThreadScrollingReason::kIsNotStackingContextAndLCDText);
+  GetWebViewImpl()->GetSettings()->SetPreferCompositingToLCDTextEnabled(false);
+
+  // Adding "contain: paint" to force a stacking context leads to promotion.
+  container->setAttribute("style", "contain: paint", ASSERT_NO_EXCEPTION);
+  ForceFullCompositingUpdate();
+
+  EXPECT_FALSE(scrollable_area->GetNonCompositedMainThreadScrollingReasons());
+}
+
 TEST_P(NonCompositedMainThreadScrollingReasonTest,
        CompositedWithLCDTextRelatedReasonsTest) {
   // With "will-change:transform" we composite elements with
   // LCDTextRelatedReasons only. For elements with other
   // NonCompositedReasons, we don't create scrollingLayer for their
   // CompositedLayerMapping therefore they don't get composited.
   GetWebViewImpl()->GetSettings()->SetPreferCompositingToLCDTextEnabled(false);
   Document* document = GetFrame()->GetDocument();
   Element* container = document->getElementById("scroller1");
   ASSERT_TRUE(container);
@@ skipping 13 matching lines @@
   ForceFullCompositingUpdate();
   PaintLayerScrollableArea* scrollable_area2 =
       ToLayoutBoxModelObject(container2->GetLayoutObject())
           ->GetScrollableArea();
   ASSERT_TRUE(scrollable_area2);
   EXPECT_TRUE(scrollable_area2->GetNonCompositedMainThreadScrollingReasons() &
               MainThreadScrollingReason::kHasBorderRadius);
 }
 
 }  // namespace blink