Only store previous clip rects for PaintLayers that support subsequences.

third_party/WebKit/Source/core/paint/PrePaintTreeWalk.cpp

 // Copyright 2015 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/PrePaintTreeWalk.h"
 
 #include "core/dom/DocumentLifecycle.h"
 #include "core/frame/FrameView.h"
 #include "core/frame/LocalFrame.h"
 #include "core/layout/LayoutMultiColumnSpannerPlaceholder.h"
@@ skipping 136 matching lines @@
   if (!object.HasLayer())
     return;
 
   PaintLayer& paint_layer = *ToLayoutBoxModelObject(object).Layer();
   if (object.StyleRef().HasTransform() ||
       &object ==
           context.paint_invalidator_context.paint_invalidation_container) {
     context.ancestor_transformed_or_root_paint_layer = &paint_layer;
   }
 
+  // This code below checks whether any clips have changed that might:
+  // (a) invalidate optimizations made for a PaintLayer that supports
+  //     subsequence caching, or
+  // (b) impact clipping of descendant visual rects.
+  if (!paint_layer.SupportsSubsequenceCaching() &&
+      !paint_layer.GetLayoutObject().HasClipRelatedProperty())
+    return;
+
   const auto& ancestor =
       context.ancestor_transformed_or_root_paint_layer->GetLayoutObject();
   PropertyTreeState ancestor_state = *ancestor.LocalBorderBoxProperties();
 
 #ifdef CHECK_CLIP_RECTS
   ShouldRespectOverflowClipType respectOverflowClip = RespectOverflowClip;
 #endif
   if (context.ancestor_transformed_or_root_paint_layer->GetCompositingState() ==
       kPaintsIntoOwnBacking) {
     const auto* ancestor_properties = ancestor.PaintProperties();
@@ skipping 135 matching lines @@
       }
       Walk(*ToFrameView(frame_view_base), context);
     }
     // TODO(pdr): Investigate RemoteFrameView (crbug.com/579281).
   }
 
   object.GetMutableForPainting().ClearPaintFlags();
 }
 
 }  // namespace blink