Only automatically promote scrollers which are untransformed and opaque.

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

Index: third_party/WebKit/Source/core/paint/PaintLayerScrollableAreaTest.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintLayerScrollableAreaTest.cpp b/third_party/WebKit/Source/core/paint/PaintLayerScrollableAreaTest.cpp
index 91ff02538bda68c7db4f954e7139b0a17cd2e738..7b28248fdb9d4ea6057c0cf4d38549998710d650 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayerScrollableAreaTest.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayerScrollableAreaTest.cpp
@@ -238,4 +238,113 @@ TEST_F(PaintLayerScrollableAreaTest, OpaqueLayersPromotedOnStyleChange) {
   ASSERT_TRUE(paintLayer->graphicsLayerBackingForScrolling());
   EXPECT_TRUE(paintLayer->graphicsLayerBackingForScrolling()->contentsOpaque());
 }
+
+// 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) {
+  RuntimeEnabledFeatures::setCompositeOpaqueScrollersEnabled(true);

[chrishtr, 2016/10/19 22:29:45]

Use the auto-resetter pattern.

[flackr, 2016/10/19 23:01:54]

Done.

+
+  setBodyInnerHTML(
+      "<style>"
+      "#scroller { overflow: scroll; height: 200px; width: 200px; background: "
+      "white local content-box; }"
+      "#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");
+  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());
+
+  // Change the parent to have a transform.
+  parent->setAttribute(HTMLNames::styleAttr, "transform: translate(1px, 0);");
+  document().view()->updateAllLifecyclePhases();
+  paintLayer = toLayoutBoxModelObject(scroller->layoutObject())->layer();
+  ASSERT_TRUE(paintLayer);
+  EXPECT_FALSE(paintLayer->needsCompositedScrolling());
+  EXPECT_FALSE(paintLayer->graphicsLayerBacking());
+
+  // Change the parent to have no transform again.
+  parent->removeAttribute(HTMLNames::styleAttr);
+  document().view()->updateAllLifecyclePhases();
+  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());
+
+  // Apply a transform to the scroller directly.
+  scroller->setAttribute(HTMLNames::styleAttr, "transform: translate(1px, 0);");
+  document().view()->updateAllLifecyclePhases();
+  paintLayer = toLayoutBoxModelObject(scroller->layoutObject())->layer();
+  ASSERT_TRUE(paintLayer);
+  EXPECT_FALSE(paintLayer->needsCompositedScrolling());
+  EXPECT_FALSE(paintLayer->graphicsLayerBacking());
+}
+
+// Test that opacity applied to the scroller or an ancestor will cause the
+// scrolling contents layer to not be promoted.
+TEST_F(PaintLayerScrollableAreaTest, OnlyOpaqueLayersPromoted) {
+  RuntimeEnabledFeatures::setCompositeOpaqueScrollersEnabled(true);
+
+  setBodyInnerHTML(
+      "<style>"
+      "#scroller { overflow: scroll; height: 200px; width: 200px; background: "
+      "white local content-box; }"
+      "#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");
+  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());
+
+  // Change the parent to be partially translucent.
+  parent->setAttribute(HTMLNames::styleAttr, "opacity: 0.5;");
+  document().view()->updateAllLifecyclePhases();
+  paintLayer = toLayoutBoxModelObject(scroller->layoutObject())->layer();
+  ASSERT_TRUE(paintLayer);
+  EXPECT_FALSE(paintLayer->needsCompositedScrolling());
+  EXPECT_FALSE(paintLayer->graphicsLayerBacking());
+
+  // Change the parent to be opaque again.
+  parent->setAttribute(HTMLNames::styleAttr, "opacity: 1;");
+  document().view()->updateAllLifecyclePhases();
+  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());
+
+  // Make the scroller translucent.
+  scroller->setAttribute(HTMLNames::styleAttr, "opacity: 0.5");
+  document().view()->updateAllLifecyclePhases();
+  paintLayer = toLayoutBoxModelObject(scroller->layoutObject())->layer();
+  ASSERT_TRUE(paintLayer);
+  EXPECT_FALSE(paintLayer->needsCompositedScrolling());
+  EXPECT_FALSE(paintLayer->graphicsLayerBacking());
+}
 }