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 1562 matching lines @@
 {
     FrameView* frameView = layoutObject->document().view();
     if (!frameView)
         return LayoutRect();
 
     return LayoutRect(frameView->visibleContentRect());
 }
 
 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()));
 
     DeprecatedPaintLayer* insideLayer = hitTestLayer(this, 0, result, hitTestArea, hitTestLocation, false);
     if (!insideLayer) {
         // We didn't hit any layer. If we are the root layer and the mouse is -- or just was -- down,
         // return ourselves. We do this so mouse events continue getting delivered after a drag has
         // exited the WebView, and so hit testing over a scrollbar hits the content document.
         // In addtion, it is possible for the mouse to stay in the document but there is no element.
         // At that time, the events of the mouse should be fired.
         LayoutPoint hitPoint = hitTestLocation.point();
         if (!request.isChildFrameHitTest() && ((request.active() || request.release()) || (request.move() && hitTestArea.contains(hitPoint.x(), hitPoint.y()))) && isRootLayer()) {
             layoutObject()->updateHitTestResult(result, toLayoutView(layoutObject())->flipForWritingMode(hitTestLocation.point()));
             insideLayer = this;
+
+            // Don't cache this result since it really wasn't a true hit.
+            result.setCacheable(false);
         }
     }
 
     // Now determine if the result is inside an anchor - if the urlElement isn't already set.
     Node* node = result.innerNode();
     if (node && !result.URLElement())
         result.setURLElement(node->enclosingLinkEventParentOrSelf());
 
     // Now return whether we were inside this layer (this will always be true for the root
     // layer).
@@ skipping 1143 matching lines @@
 
 void showLayerTree(const blink::LayoutObject* layoutObject)
 {
     if (!layoutObject) {
         fprintf(stderr, "Cannot showLayerTree. Root is (nil)\n");
         return;
     }
     showLayerTree(layoutObject->enclosingLayer());
 }
 #endif