Move computation of RenderLayer::isUnclippedDescendant into CompositingPropertyUpdater

Source/core/rendering/compositing/CompositingReasonFinder.cpp

 // Copyright 2014 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 "config.h"
 #include "core/rendering/compositing/CompositingReasonFinder.h"
 
 #include "CSSPropertyNames.h"
 #include "HTMLNames.h"
 #include "core/frame/FrameView.h"
@@ skipping 124 matching lines @@
 
     return renderer->hasFilter();
 }
 
 CompositingReasons CompositingReasonFinder::nonStyleDeterminedDirectReasons(const RenderLayer* layer, bool* needToRecomputeCompositingRequirements) const
 {
     CompositingReasons directReasons = CompositingReasonNone;
     RenderObject* renderer = layer->renderer();
 
     if (hasOverflowScrollTrigger()) {
-        if (layer->isUnclippedDescendant())
+        // IsUnclippedDescendant is only actually stale during the chicken/egg code path.
+        // FIXME: Use ancestorDependentProperties().isUnclippedDescendant to ASSERT that
+        // this value isn't stale.

[Ian Vollick, 2014/06/01 19:25:36]

What would you think of using the disabler here?

[abarth-chromium, 2014/06/01 19:49:36]

There isn't a disabler for this ASSERT because it's guarding the inputs to the
computing update rather than the outputs.  Hopefully there won't be any more
violations...

This would be clearer if we renamed ancestorDependentProperties() to
compositingInputs()    :)

+        if (layer->potentiallyStaleIsUnclippedDescendant())
             directReasons |= CompositingReasonOutOfFlowClipping;
 
         if (layer->scrollParent())
             directReasons |= CompositingReasonOverflowScrollingParent;
 
         if (layer->needsCompositedScrolling())
             directReasons |= CompositingReasonOverflowScrollingTouch;
     }
 
     if (requiresCompositingForPositionSticky(renderer, layer))
@@ skipping 101 matching lines @@
             if (viewportConstrainedNotCompositedReason)
                 *viewportConstrainedNotCompositedReason = RenderLayer::NotCompositedForBoundsOutOfView;
             return false;
         }
     }
 
     return true;
 }
 
 }