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 81f29ebe4fcb059286468123362ea893c1637fc0..2b6ca80af97fc882a51a81a5b927ac6938ca2c31 100644
--- a/Source/core/paint/DeprecatedPaintLayer.cpp
+++ b/Source/core/paint/DeprecatedPaintLayer.cpp
@@ -1646,21 +1646,20 @@ static inline LayoutRect frameVisibleRect(LayoutObject* layoutObject)
 
 bool DeprecatedPaintLayer::hitTest(HitTestResult& result)
 {
-    return hitTest(result.hitTestRequest(), result.hitTestLocation(), result);
-}
-
-bool DeprecatedPaintLayer::hitTest(const HitTestRequest& request, const HitTestLocation& hitTestLocation, HitTestResult& result)
-{
     ASSERT(isSelfPaintingLayer() || hasSelfPaintingLayerDescendant());
 
     // LayoutView should make sure to update layout before entering hit testing
     ASSERT(!layoutObject()->frame()->view()->layoutPending());
     ASSERT(!layoutObject()->document().layoutView()->needsLayout());
 
+    const HitTestRequest& request = result.hitTestRequest();
+    const HitTestLocation& hitTestLocation = result.hitTestLocation();
+
     // Start with frameVisibleRect to ensure we include the scrollbars.
     LayoutRect hitTestArea = frameVisibleRect(layoutObject());
     if (request.ignoreClipping())
         hitTestArea.unite(LayoutRect(layoutObject()->view()->documentRect()));
+    result.setValidityRect(boundingRect(hitTestLocation.point()));
 
     DeprecatedPaintLayer* insideLayer = hitTestLayer(this, 0, result, hitTestArea, hitTestLocation, false);
     if (!insideLayer) {
@@ -1896,6 +1895,7 @@ 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())) {
@@ -1927,6 +1927,7 @@ 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())) {
@@ -2081,6 +2082,7 @@ DeprecatedPaintLayer* DeprecatedPaintLayer::hitTestChildren(ChildrenIteration ch
         DeprecatedPaintLayer* childLayer = child->layer();
         DeprecatedPaintLayer* hitLayer = 0;
         HitTestResult tempResult(result.hitTestRequest(), result.hitTestLocation());
+        tempResult.setValidityRect(result.validityRect());
         if (childLayer->isPaginated())
             hitLayer = hitTestPaginatedChildLayer(childLayer, rootLayer, tempResult, hitTestRect, hitTestLocation, transformState, zOffsetForDescendants);
         else