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

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

 // Copyright 2016 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/paint/PaintLayerScrollableArea.h"
 
 #include "core/frame/FrameView.h"
 #include "core/layout/LayoutBoxModelObject.h"
 #include "core/layout/LayoutTestHelper.h"
 #include "core/paint/PaintLayer.h"
@@ skipping 137 matching lines @@
   // #scroller15 cannot paint background into scrolling contents layer because
   // the outline is drawn inside the padding box.
   EXPECT_FALSE(canPaintBackgroundOntoScrollingContentsLayer("scroller15"));
 
   // #scroller16 cannot paint background into scrolling contents layer because
   // the scroller has a clip which would not be respected by the scrolling
   // contents layer.
   EXPECT_FALSE(canPaintBackgroundOntoScrollingContentsLayer("scroller16"));
 }
 
-TEST_F(PaintLayerScrollableAreaTest, OpaqueLayersPromoted) {
+TEST_F(PaintLayerScrollableAreaTest, OpaqueContainedLayersPromoted) {
   RuntimeEnabledFeatures::setCompositeOpaqueScrollersEnabled(true);
 
   setBodyInnerHTML(
       "<style>"
-      "#scroller { overflow: scroll; height: 200px; width: 200px; background: "
-      "white local content-box; border: 10px solid rgba(0, 255, 0, 0.5); }"
+      "#scroller { overflow: scroll; height: 200px; width: 200px; "
+      "contain: paint; background: white local content-box; "
+      "border: 10px solid rgba(0, 255, 0, 0.5); }"
       "#scrolled { height: 300px; }"
       "</style>"
       "<div id=\"scroller\"><div id=\"scrolled\"></div></div>");
   document().view()->updateAllLifecyclePhases();
 
   EXPECT_TRUE(RuntimeEnabledFeatures::compositeOpaqueScrollersEnabled());
   Element* scroller = document().getElementById("scroller");
   PaintLayer* paintLayer =
       toLayoutBoxModelObject(scroller->layoutObject())->layer();
   ASSERT_TRUE(paintLayer);
   EXPECT_TRUE(paintLayer->needsCompositedScrolling());
   EXPECT_TRUE(paintLayer->graphicsLayerBacking());
   ASSERT_TRUE(paintLayer->graphicsLayerBackingForScrolling());
   EXPECT_TRUE(paintLayer->graphicsLayerBackingForScrolling()->contentsOpaque());
 }
 
+// Tests that we don't promote scrolling content which would not be contained.
+// Promoting the scroller would also require promoting the positioned div
+// which would lose subpixel anti-aliasing due to its transparent background.
+TEST_F(PaintLayerScrollableAreaTest, NonContainedLayersNotPromoted) {
+  RuntimeEnabledFeatures::setCompositeOpaqueScrollersEnabled(true);
+
+  setBodyInnerHTML(
+      "<style>"
+      "#scroller { overflow: scroll; height: 200px; width: 200px; "
+      "background: white local content-box; "
+      "border: 10px solid rgba(0, 255, 0, 0.5); }"
+      "#scrolled { height: 300px; }"
+      "#positioned { position: relative; }"
+      "</style>"
+      "<div id=\"scroller\">"
+      "  <div id=\"positioned\">Not contained by scroller.</div>"
+      "  <div id=\"scrolled\"></div>"
+      "</div>");
+  document().view()->updateAllLifecyclePhases();
+
+  EXPECT_TRUE(RuntimeEnabledFeatures::compositeOpaqueScrollersEnabled());
+  Element* scroller = document().getElementById("scroller");
+  PaintLayer* paintLayer =
+      toLayoutBoxModelObject(scroller->layoutObject())->layer();
+  ASSERT_TRUE(paintLayer);
+  EXPECT_FALSE(paintLayer->needsCompositedScrolling());
+  EXPECT_FALSE(paintLayer->graphicsLayerBacking());
+  EXPECT_FALSE(paintLayer->graphicsLayerBackingForScrolling());
+}
+
 TEST_F(PaintLayerScrollableAreaTest, TransparentLayersNotPromoted) {
   RuntimeEnabledFeatures::setCompositeOpaqueScrollersEnabled(true);
 
   setBodyInnerHTML(
       "<style>"
       "#scroller { overflow: scroll; height: 200px; width: 200px; background: "
       "rgba(0, 255, 0, 0.5) local content-box; border: 10px solid rgba(0, 255, "
-      "0, 0.5); }"
+      "0, 0.5); contain: paint; }"
       "#scrolled { height: 300px; }"
       "</style>"
       "<div id=\"scroller\"><div id=\"scrolled\"></div></div>");
   document().view()->updateAllLifecyclePhases();
 
   EXPECT_TRUE(RuntimeEnabledFeatures::compositeOpaqueScrollersEnabled());
   Element* scroller = document().getElementById("scroller");
   PaintLayer* paintLayer =
       toLayoutBoxModelObject(scroller->layoutObject())->layer();
   ASSERT_TRUE(paintLayer);
   EXPECT_FALSE(paintLayer->needsCompositedScrolling());
   EXPECT_FALSE(paintLayer->graphicsLayerBacking());
   EXPECT_FALSE(paintLayer->graphicsLayerBackingForScrolling());
 }
 
 TEST_F(PaintLayerScrollableAreaTest, OpaqueLayersDepromotedOnStyleChange) {
   RuntimeEnabledFeatures::setCompositeOpaqueScrollersEnabled(true);
 
   setBodyInnerHTML(
       "<style>"
       "#scroller { overflow: scroll; height: 200px; width: 200px; background: "
-      "white local content-box; }"
+      "white local content-box; contain: paint; }"
       "#scrolled { height: 300px; }"
       "</style>"
       "<div id=\"scroller\"><div id=\"scrolled\"></div></div>");
   document().view()->updateAllLifecyclePhases();
 
   EXPECT_TRUE(RuntimeEnabledFeatures::compositeOpaqueScrollersEnabled());
   Element* scroller = document().getElementById("scroller");
   PaintLayer* paintLayer =
       toLayoutBoxModelObject(scroller->layoutObject())->layer();
   ASSERT_TRUE(paintLayer);
@@ skipping 10 matching lines @@
   EXPECT_FALSE(paintLayer->graphicsLayerBacking());
   EXPECT_FALSE(paintLayer->graphicsLayerBackingForScrolling());
 }
 
 TEST_F(PaintLayerScrollableAreaTest, OpaqueLayersPromotedOnStyleChange) {
   RuntimeEnabledFeatures::setCompositeOpaqueScrollersEnabled(true);
 
   setBodyInnerHTML(
       "<style>"
       "#scroller { overflow: scroll; height: 200px; width: 200px; background: "
-      "rgba(255,255,255,0.5) local content-box; }"
+      "rgba(255,255,255,0.5) local content-box; contain: paint; }"
       "#scrolled { height: 300px; }"
       "</style>"
       "<div id=\"scroller\"><div id=\"scrolled\"></div></div>");
   document().view()->updateAllLifecyclePhases();
 
   EXPECT_TRUE(RuntimeEnabledFeatures::compositeOpaqueScrollersEnabled());
   Element* scroller = document().getElementById("scroller");
   PaintLayer* paintLayer =
       toLayoutBoxModelObject(scroller->layoutObject())->layer();
   ASSERT_TRUE(paintLayer);
@@ skipping 13 matching lines @@
 
 // Tests that a transform on the scroller or an ancestor will prevent promotion
 // TODO(flackr): Allow integer transforms as long as all of the ancestor
 // transforms are also integer.
 TEST_F(PaintLayerScrollableAreaTest, OnlyNonTransformedOpaqueLayersPromoted) {
   ScopedCompositeOpaqueScrollersForTest compositeOpaqueScrollers(true);
 
   setBodyInnerHTML(
       "<style>"
       "#scroller { overflow: scroll; height: 200px; width: 200px; background: "
-      "white local content-box; }"
+      "white local content-box; contain: paint; }"
       "#scrolled { height: 300px; }"
       "</style>"
       "<div id=\"parent\">"
       "  <div id=\"scroller\"><div id=\"scrolled\"></div></div>"
       "</div>");
   document().view()->updateAllLifecyclePhases();
 
   EXPECT_TRUE(RuntimeEnabledFeatures::compositeOpaqueScrollersEnabled());
   Element* parent = document().getElementById("parent");
   Element* scroller = document().getElementById("scroller");
@@ skipping 33 matching lines @@
 }
 
 // Test that opacity applied to the scroller or an ancestor will cause the
 // scrolling contents layer to not be promoted.
 TEST_F(PaintLayerScrollableAreaTest, OnlyOpaqueLayersPromoted) {
   ScopedCompositeOpaqueScrollersForTest compositeOpaqueScrollers(true);
 
   setBodyInnerHTML(
       "<style>"
       "#scroller { overflow: scroll; height: 200px; width: 200px; background: "
-      "white local content-box; }"
+      "white local content-box; contain: paint; }"
       "#scrolled { height: 300px; }"
       "</style>"
       "<div id=\"parent\">"
       "  <div id=\"scroller\"><div id=\"scrolled\"></div></div>"
       "</div>");
   document().view()->updateAllLifecyclePhases();
 
   EXPECT_TRUE(RuntimeEnabledFeatures::compositeOpaqueScrollersEnabled());
   Element* parent = document().getElementById("parent");
   Element* scroller = document().getElementById("scroller");
@@ skipping 60 matching lines @@
   ASSERT_TRUE(blackLayer);
 
   ASSERT_EQ(ScrollbarOverlayColorTheme::ScrollbarOverlayColorThemeDark,
             noneLayer->getScrollableArea()->getScrollbarOverlayColorTheme());
   ASSERT_EQ(ScrollbarOverlayColorTheme::ScrollbarOverlayColorThemeDark,
             whiteLayer->getScrollableArea()->getScrollbarOverlayColorTheme());
   ASSERT_EQ(ScrollbarOverlayColorTheme::ScrollbarOverlayColorThemeLight,
             blackLayer->getScrollableArea()->getScrollbarOverlayColorTheme());
 }
 }