Implement a Hit Test Cache.

Source/core/paint/DeprecatedPaintLayer.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
  *   Randall Jesup <rjesup@wgate.com>
@@ skipping 1761 matching lines @@
     if (m_scrollableArea && m_scrollableArea->hitTestResizerInFragments(layerFragments, hitTestLocation)) {
         layoutObject()->updateHitTestResult(result, hitTestLocation.point());
         return this;
     }
 
     // Next we want to see if the mouse pos is inside the child LayoutObjects of the layer. Check
     // every fragment in reverse order.
     if (isSelfPaintingLayer()) {
         // Hit test with a temporary HitTestResult, because we only want to commit to 'result' if we know we're frontmost.
         HitTestResult tempResult(result.hitTestRequest(), result.hitTestLocation());
+        tempResult.setValidityRect(result.validityRect());
         bool insideFragmentForegroundRect = false;
         if (hitTestContentsForFragments(layerFragments, tempResult, hitTestLocation, HitTestDescendants, insideFragmentForegroundRect)
             && isHitCandidate(this, false, zOffsetForContentsPtr, unflattenedTransformState.get())) {
             if (result.hitTestRequest().listBased())
                 result.append(tempResult);
             else
                 result = tempResult;
             if (!depthSortDescendants)
                 return this;
             // Foreground can depth-sort with descendant layers, so keep this as a candidate.
@@ skipping 11 matching lines @@
             return hitLayer;
         candidateLayer = hitLayer;
     }
 
     // If we found a layer, return. Child layers, and foreground always render in front of background.
     if (candidateLayer)
         return candidateLayer;
 
     if (isSelfPaintingLayer()) {
         HitTestResult tempResult(result.hitTestRequest(), result.hitTestLocation());
+        tempResult.setValidityRect(result.validityRect());
         bool insideFragmentBackgroundRect = false;
         if (hitTestContentsForFragments(layerFragments, tempResult, hitTestLocation, HitTestSelf, insideFragmentBackgroundRect)
             && isHitCandidate(this, false, zOffsetForContentsPtr, unflattenedTransformState.get())) {
             if (result.isRectBasedTest())
                 result.append(tempResult);
             else
                 result = tempResult;
             return this;
         }
         if (insideFragmentBackgroundRect && result.hitTestRequest().listBased())
@@ skipping 134 matching lines @@
 {
     if (!hasSelfPaintingLayerDescendant())
         return 0;
 
     DeprecatedPaintLayer* resultLayer = 0;
     DeprecatedPaintLayerStackingNodeReverseIterator iterator(*m_stackingNode, childrentoVisit);
     while (DeprecatedPaintLayerStackingNode* child = iterator.next()) {
         DeprecatedPaintLayer* childLayer = child->layer();
         DeprecatedPaintLayer* hitLayer = 0;
         HitTestResult tempResult(result.hitTestRequest(), result.hitTestLocation());
+        tempResult.setValidityRect(result.validityRect());
         hitLayer = childLayer->hitTestLayer(rootLayer, this, tempResult, hitTestRect, hitTestLocation, false, transformState, zOffsetForDescendants);
 
         // If it is a list-based test, we can safely append the temporary result since it might had hit
         // nodes but not necesserily had hitLayer set.
         ASSERT(!result.isRectBasedTest() || result.hitTestRequest().listBased());
         if (result.hitTestRequest().listBased())
             result.append(tempResult);
 
         if (isHitCandidate(hitLayer, depthSortDescendants, zOffset, unflattenedTransformState)) {
             resultLayer = hitLayer;
@@ skipping 735 matching lines @@
 
 void showLayerTree(const blink::LayoutObject* layoutObject)
 {
     if (!layoutObject) {
         fprintf(stderr, "Cannot showLayerTree. Root is (nil)\n");
         return;
     }
     showLayerTree(layoutObject->enclosingLayer());
 }
 #endif