Implement a Hit Test Cache.

Source/core/paint/DeprecatedPaintLayer.cpp

Index: Source/core/paint/DeprecatedPaintLayer.cpp
diff --git a/Source/core/paint/DeprecatedPaintLayer.cpp b/Source/core/paint/DeprecatedPaintLayer.cpp
index 1dfe90db5c0961677ec07cc28d1385464276021f..644c33856ffd0d87af382039781a03ef1ff9d0ec 100644
--- a/Source/core/paint/DeprecatedPaintLayer.cpp
+++ b/Source/core/paint/DeprecatedPaintLayer.cpp
@@ -1779,6 +1779,7 @@ DeprecatedPaintLayer* DeprecatedPaintLayer::hitTestLayer(DeprecatedPaintLayer* r
     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())) {
@@ -1810,6 +1811,7 @@ DeprecatedPaintLayer* DeprecatedPaintLayer::hitTestLayer(DeprecatedPaintLayer* r
 
     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())) {
@@ -1964,6 +1966,7 @@ DeprecatedPaintLayer* DeprecatedPaintLayer::hitTestChildren(ChildrenIteration ch
         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