Reland "Box shadow should be recorded as main thread scrolling reasons for non-root layers."

third_party/WebKit/Source/web/tests/ScrollingCoordinatorTest.cpp

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
  *     notice, this list of conditions and the following disclaimer in the
@@ skipping 1137 matching lines @@
   forceFullCompositingUpdate();
   ASSERT_FALSE(frameView->mainThreadScrollingReasons() & reason);
 }
 
 TEST_F(StyleRelatedMainThreadScrollingReasonTest, LCDTextEnabledTest) {
   testStyle("transparent border-radius",
             MainThreadScrollingReason::kHasOpacityAndLCDText |
                 MainThreadScrollingReason::kHasBorderRadius);
 }
 
+TEST_F(StyleRelatedMainThreadScrollingReasonTest, BoxShadowTest) {
+  testStyle("box-shadow",
+            MainThreadScrollingReason::kHasBoxShadowFromNonRootLayer);
+}
+
 }  // namespace blink