Fix the bug that negative outline-offset is covered up by composited

third_party/WebKit/Source/core/layout/compositing/CompositedLayerMappingTest.cpp

Index: third_party/WebKit/Source/core/layout/compositing/CompositedLayerMappingTest.cpp
diff --git a/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMappingTest.cpp b/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMappingTest.cpp
index 22b69f679c0e5f21ec526f9ac6e97a7168158c83..e9daa71b29543e898870c578fe00c122de9063df 100644
--- a/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMappingTest.cpp
+++ b/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMappingTest.cpp
@@ -837,6 +837,69 @@ TEST_P(CompositedLayerMappingTest,
 }
 
 TEST_P(CompositedLayerMappingTest,
+       DecorationLayerOnlyCreatedInCompositedScrolling) {
+  setBodyInnerHTML(
+      "<div id='target' style='height: 200px; "
+      "will-change: transform;'></div>");

[flackr, 2016/11/17 16:10:45]

This element should have a negative offset outline such that if it were a
composited scroller it would get a decoration layer. Perhaps the test could
actually verify that it does by switching from overflow: visible to overflow:
scroll.

[yigu, 2016/11/18 04:14:07]

Done.

+  document().view()->updateAllLifecyclePhases();
+
+  Element* element = document().getElementById("target");
+  PaintLayer* paintLayer =
+      toLayoutBoxModelObject(element->layoutObject())->layer();
+  ASSERT_TRUE(paintLayer);
+
+  // No decoration layer is created when not composited scrolling.
+  EXPECT_TRUE(paintLayer->hasCompositedLayerMapping());
+  EXPECT_FALSE(paintLayer->needsCompositedScrolling());
+
+  CompositedLayerMapping* mapping = paintLayer->compositedLayerMapping();
+  EXPECT_FALSE(mapping->decorationLayer());
+}
+
+TEST_P(CompositedLayerMappingTest,
+       DecorationLayerCreatedAndDestroyedInCompositedScrolling) {
+  setBodyInnerHTML(
+      "<style>"
+      "#scroller { overflow: scroll; height: 200px; width: 200px; background: "
+      "white local content-box; outline: 1px solid blue;}"
+      "#scrolled { height: 300px; }"
+      "</style>"
+      "<div id=\"parent\">"
+      "  <div id=\"scroller\"><div id=\"scrolled\"></div></div>"
+      "</div>");
+  document().view()->updateAllLifecyclePhases();
+
+  Element* scroller = document().getElementById("scroller");
+  PaintLayer* paintLayer =
+      toLayoutBoxModelObject(scroller->layoutObject())->layer();
+  ASSERT_TRUE(paintLayer);
+
+  CompositedLayerMapping* mapping = paintLayer->compositedLayerMapping();
+  EXPECT_FALSE(mapping->decorationLayer());
+
+  // The decoration layer is created when composited scrolling
+  // with an outline drawn over the composited scrolling region.
+  scroller->setAttribute(HTMLNames::styleAttr, "outline-offset: -2px;");
+  document().view()->updateAllLifecyclePhases();
+  paintLayer = toLayoutBoxModelObject(scroller->layoutObject())->layer();
+  ASSERT_TRUE(paintLayer);
+
+  mapping = paintLayer->compositedLayerMapping();
+  EXPECT_TRUE(paintLayer->needsCompositedScrolling());
+  EXPECT_TRUE(mapping->decorationLayer());
+
+  // The decoration layer is destroyed when the scrolling region
+  // will not be covered up by the outline.
+  scroller->removeAttribute(HTMLNames::styleAttr);
+  document().view()->updateAllLifecyclePhases();
+  paintLayer = toLayoutBoxModelObject(scroller->layoutObject())->layer();
+  ASSERT_TRUE(paintLayer);
+
+  mapping = paintLayer->compositedLayerMapping();
+  EXPECT_FALSE(mapping->decorationLayer());
+}
+
+TEST_P(CompositedLayerMappingTest,
        BackgroundPaintedIntoGraphicsLayerIfNotCompositedScrolling) {
   document().frame()->settings()->setPreferCompositingToLCDTextEnabled(true);
   setBodyInnerHTML(