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

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 127 matching lines @@
   EXPECT_FALSE(canPaintBackgroundOntoScrollingContentsLayer("scroller12"));
 
   // #scroller13 cannot paint background into scrolling contents layer because
   // it has a custom scrollbar which the background may need to draw under.
   EXPECT_FALSE(canPaintBackgroundOntoScrollingContentsLayer("scroller13"));
 
   // #scroller14 can paint background into scrolling contents layer because the
   // outline is drawn outside the padding box.
   EXPECT_TRUE(canPaintBackgroundOntoScrollingContentsLayer("scroller14"));
 
-  // #scroller15 cannot paint background into scrolling contents layer because
-  // the outline is drawn inside the padding box.
-  EXPECT_FALSE(canPaintBackgroundOntoScrollingContentsLayer("scroller15"));
+  // #scroller15 can paint background into scrolling contents layer because
+  // the outline is drawn into the decoration layer which will not be covered
+  // up.
+  EXPECT_TRUE(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) {
   RuntimeEnabledFeatures::setCompositeOpaqueScrollersEnabled(true);
 
@@ skipping 239 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());
 }
 }