Fix unexpected blurry text caused by combination of skew and promotion

third_party/WebKit/Source/core/layout/compositing/CompositingReasonFinderTest.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/layout/compositing/CompositingReasonFinder.h"
 
 #include "core/frame/FrameView.h"
 #include "core/layout/LayoutBlock.h"
 #include "core/layout/LayoutTestHelper.h"
 #include "core/paint/PaintLayer.h"
@@ skipping 285 matching lines @@
 
   Element* innerSticky = document().getElementById("innerSticky");
   PaintLayer* innerStickyLayer =
       toLayoutBoxModelObject(innerSticky->layoutObject())->layer();
   ASSERT_TRUE(innerStickyLayer);
 
   EXPECT_EQ(PaintsIntoOwnBacking, outerStickyLayer->compositingState());
   EXPECT_EQ(NotComposited, innerStickyLayer->compositingState());
 }
 
+TEST_F(CompositingReasonFinderTest, CompositeSkewWithPromotedSkewedAncestor) {
+  setBodyInnerHTML(
+      "<style>div.skew { transform: skew(20deg);}"
+      "div.skew > div { transform: skew(-20deg); }"
+      "div.composited { will-change: transform; }</style>"
+      "<div class='skew'>"
+      "  <div id='non-composited'></div>"
+      "</div>"
+      "<div id='skew' class='skew'>"
+      "  <div id='should-composite'></div>"
+      "  <div id='composited' class='composited'></div>"
+      "</div>");
+  document().view()->updateAllLifecyclePhases();
+
+  // Skewed element is not composited automatically.
+  Element* nonComposited = document().getElementById("non-composited");
+  PaintLayer* nonCompositedLayer =
+      toLayoutBoxModelObject(nonComposited->layoutObject())->layer();
+  ASSERT_TRUE(nonCompositedLayer);
+  EXPECT_EQ(NotComposited, nonCompositedLayer->compositingState());
+
+  // Composite as it has composited descendant.
+  Element* compositedElement = document().getElementById("skew");
+  PaintLayer* compositedLayer =
+      toLayoutBoxModelObject(compositedElement->layoutObject())->layer();
+  ASSERT_TRUE(compositedLayer);
+  EXPECT_EQ(PaintsIntoOwnBacking, compositedLayer->compositingState());

[flackr, 2017/02/28 21:40:14]

This should not automatically be composited, it's only if #skew is composited
that we would composite its children because they are also skewed.

+
+  // Skewed element with promoted skewed ancestor gets promoted as well.
+  compositedElement = document().getElementById("should-composite");
+  compositedLayer =
+      toLayoutBoxModelObject(compositedElement->layoutObject())->layer();
+  ASSERT_TRUE(compositedLayer);
+  EXPECT_EQ(PaintsIntoOwnBacking, compositedLayer->compositingState());
+
+  // Skewed element without promoted ancestor does not composite.
+  document().getElementById("composited")->removeAttribute("class");
+  document().view()->updateAllLifecyclePhases();
+  ASSERT_TRUE(compositedLayer);
+  EXPECT_EQ(NotComposited, compositedLayer->compositingState());
+
+  // Skewed element with promoted ancestor which is not skewed does not
+  // composite.
+  document()
+      .getElementById("composited")
+      ->setAttribute(HTMLNames::classAttr, "composited");
+  document().getElementById("skew")->removeAttribute("class");
+  document().view()->updateAllLifecyclePhases();
+  ASSERT_TRUE(compositedLayer);
+  EXPECT_EQ(NotComposited, compositedLayer->compositingState());
+}
+
 }  // namespace blink