Enable compositing for opaque scrolling content on low DPI screens

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
new file mode 100644
index 0000000000000000000000000000000000000000..f11b78585bf5bbf4aa33df3d6d844357746ec8e4
--- /dev/null
+++ b/third_party/WebKit/Source/core/paint/PaintLayerScrollableAreaTest.cpp
@@ -0,0 +1,47 @@
+// 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/PaintLayerScrollableAreaTest.h"
+
+namespace blink {
+
+TEST_F(PaintLayerScrollableAreaTest, OpaqueLayersPromoted)
+{
+    RuntimeEnabledFeatures::setCompositeOpaqueScrollersEnabled(true);
+
+    setBodyInnerHTML(
+        "<style>"
+        "#scroller { overflow: scroll; height: 300px; width: 300px; background-color: rgb(0,128,0); }"
+        "#scrolled { height: 1000px; width: 250px; }"
+        "</style>"
+        "<div id=\"scroller\"><div id=\"scrolled\"></div></div>");
+    document().view()->updateAllLifecyclePhases();
+
+    ASSERT_TRUE(RuntimeEnabledFeatures::compositeOpaqueScrollersEnabled());
+    Element* scroller = document().getElementById("scroller");
+    PaintLayer* paintLayer = toLayoutBoxModelObject(scroller->layoutObject())->layer();
+    ASSERT_TRUE(paintLayer);
+    ASSERT_TRUE(paintLayer->needsCompositedScrolling());
+}
+
+TEST_F(PaintLayerScrollableAreaTest, TransparentLayersNotPromoted)
+{
+    RuntimeEnabledFeatures::setCompositeOpaqueScrollersEnabled(true);
+
+    setBodyInnerHTML(
+        "<style>"
+        "#scroller { overflow: scroll; height: 300px; width: 300px; background-color: rgba(0,128,0,0.5); }"
+        "#scrolled { height: 1000px; width: 250px; }"
+        "</style>"
+        "<div id=\"scroller\"><div id=\"scrolled\"></div></div>");
+    document().view()->updateAllLifecyclePhases();
+
+    ASSERT_TRUE(RuntimeEnabledFeatures::compositeOpaqueScrollersEnabled());
+    Element* scroller = document().getElementById("scroller");
+    PaintLayer* paintLayer = toLayoutBoxModelObject(scroller->layoutObject())->layer();
+    ASSERT_TRUE(paintLayer);
+    ASSERT_TRUE(!paintLayer->needsCompositedScrolling());
+}
+
+}