Only store previous clip rects for PaintLayers that support subsequences.

third_party/WebKit/Source/core/paint/PaintInvalidator.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/PaintInvalidator.h"
 
 #include "core/editing/FrameSelection.h"
 #include "core/frame/FrameView.h"
 #include "core/frame/LocalFrame.h"
 #include "core/frame/Settings.h"
@@ skipping 484 matching lines @@
         PaintInvalidatorContext::kForcedSubtreeInvalidationChecking;
   }
 
   if (context.forced_subtree_invalidation_flags &&
       context.NeedsVisualRectUpdate(object)) {
     // If any subtree flag is set, we also need to pass needsVisualRectUpdate
     // requirement to the subtree.
     context.forced_subtree_invalidation_flags |=
         PaintInvalidatorContext::kForcedSubtreeVisualRectUpdate;
   }
+
+  bool usesCompositedScrolling = false;
+  if (!RuntimeEnabledFeatures::slimmingPaintV2Enabled() &&

[pdr., 2017/04/13 16:21:45]

Why do we need !RuntimeEnabledFeatures::slimmingPaintV2Enabled() here and on
line 511?

[chrishtr, 2017/04/13 17:15:38]

Because if SPv2 is on, we don't map visual rects through ancestor clips. That
happens
later in PAC.

+      object.IsBoxModelObject() &&
+      ToLayoutBoxModelObject(object).UsesCompositedScrolling())
+    usesCompositedScrolling = true;
+  if (!RuntimeEnabledFeatures::slimmingPaintV2Enabled() &&
+      context.old_visual_rect != object.VisualRect() &&
+      !usesCompositedScrolling
+      // Note that isLayoutView() below becomes unnecessary after the launch of
+      // root layer scrolling.
+      && (object.HasOverflowClip() || object.IsLayoutView())) {
+    // Changes to clipping may affect any descendant.
+    context.forced_subtree_invalidation_flags |=
+        PaintInvalidatorContext::kForcedSubtreeVisualRectUpdate;
+  }
 }
 
 void PaintInvalidator::ProcessPendingDelayedPaintInvalidations() {
   for (auto target : pending_delayed_paint_invalidations_) {
     target->GetMutableForPainting().SetShouldDoFullPaintInvalidation(
         kPaintInvalidationDelayedFull);
   }
 }
 
 }  // namespace blink