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

cc/input/main_thread_scrolling_reason.h

 // 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.
 
 #ifndef CC_INPUT_MAIN_THREAD_SCROLLING_REASON_H_
 #define CC_INPUT_MAIN_THREAD_SCROLLING_REASON_H_
 
 #include <string>
 
 #include "base/trace_event/trace_event_argument.h"
@@ skipping 23 matching lines @@
 
     // Style-related scrolling on main reasons.
     // These *AndLCDText reasons are due to subpixel text rendering which can
     // only be applied by blending glyphs with the background at a specific
     // screen position; transparency and transforms break this.
     kHasOpacityAndLCDText = 1 << 16,
     kHasTransformAndLCDText = 1 << 17,
     kBackgroundNotOpaqueInRectAndLCDText = 1 << 18,
     kHasBorderRadius = 1 << 19,
     kHasClipRelatedProperty = 1 << 20,
+    kHasBoxShadowFromNonRootLayer = 1 << 21,
 
     // Transient scrolling reasons. These are computed for each scroll begin.
     kNonFastScrollableRegion = 1 << 5,
     kFailedHitTest = 1 << 7,
     kNoScrollingLayer = 1 << 8,
     kNotScrollable = 1 << 9,
     kContinuingMainThreadScroll = 1 << 10,
     kNonInvertibleTransform = 1 << 11,
     kPageBasedScrolling = 1 << 12,
 
     // The maximum number of flags in this struct (excluding itself).
     // New flags should increment this number but it should never be decremented
     // because the values are used in UMA histograms. It should also be noted
     // that it excludes the kNotScrollingOnMain value.
-    kMainThreadScrollingReasonCount = 21,
+    kMainThreadScrollingReasonCount = 22,
   };
 
   // Returns true if the given MainThreadScrollingReason can be set by the main
   // thread.
   static bool MainThreadCanSetScrollReasons(uint32_t reasons) {
     uint32_t reasons_set_by_main_thread =
         kNotScrollingOnMain | kHasBackgroundAttachmentFixedObjects |
         kHasNonLayerViewportConstrainedObjects | kThreadedScrollingDisabled |
         kScrollbarScrolling | kPageOverlay | kHandlingScrollFromMainThread |
         kCustomScrollbarScrolling | kHasOpacityAndLCDText |
         kHasTransformAndLCDText | kBackgroundNotOpaqueInRectAndLCDText |
-        kHasBorderRadius | kHasClipRelatedProperty;
+        kHasBorderRadius | kHasClipRelatedProperty |
+        kHasBoxShadowFromNonRootLayer;
     return (reasons & reasons_set_by_main_thread) == reasons;
   }
 
   // Returns true if the given MainThreadScrollingReason can be set by the
   // compositor.
   static bool CompositorCanSetScrollReasons(uint32_t reasons) {
     uint32_t reasons_set_by_compositor =
         kNonFastScrollableRegion | kFailedHitTest | kNoScrollingLayer |
         kNotScrollable | kContinuingMainThreadScroll | kNonInvertibleTransform |
         kPageBasedScrolling;
@@ skipping 37 matching lines @@
       tracedValue->AppendString("Has transform and LCD text");
     if (reasons &
         MainThreadScrollingReason::kBackgroundNotOpaqueInRectAndLCDText) {
       tracedValue->AppendString(
           "Background is not opaque in rect and LCD text");
     }
     if (reasons & MainThreadScrollingReason::kHasBorderRadius)
       tracedValue->AppendString("Has border radius");
     if (reasons & MainThreadScrollingReason::kHasClipRelatedProperty)
       tracedValue->AppendString("Has clip related property");
+    if (reasons & MainThreadScrollingReason::kHasBoxShadowFromNonRootLayer)
+      tracedValue->AppendString("Has box shadow from non-root layer");
 
     // Transient scrolling reasons.
     if (reasons & MainThreadScrollingReason::kNonFastScrollableRegion)
       tracedValue->AppendString("Non fast scrollable region");
     if (reasons & MainThreadScrollingReason::kFailedHitTest)
       tracedValue->AppendString("Failed hit test");
     if (reasons & MainThreadScrollingReason::kNoScrollingLayer)
       tracedValue->AppendString("No scrolling layer");
     if (reasons & MainThreadScrollingReason::kNotScrollable)
       tracedValue->AppendString("Not scrollable");
@@ skipping 17 matching lines @@
       reason = reason >> 1;
       ++index;
     }
     return index;
   }
 };
 
 }  // namespace cc
 
 #endif  // CC_INPUT_MAIN_THREAD_SCROLLING_REASON_H_