Implement a Hit Test Cache.

Source/core/layout/line/LineBoxList.cpp

 /*
  * Copyright (C) 2008 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 191 matching lines @@
 
     // If we have no lines then we have no work to do.
     if (!firstLineBox())
         return false;
 
     LayoutPoint point = locationInContainer.point();
     LayoutRect rect(firstLineBox()->isHorizontal() ?
         IntRect(point.x(), point.y() - locationInContainer.topPadding(), 1, locationInContainer.topPadding() + locationInContainer.bottomPadding() + 1) :
         IntRect(point.x() - locationInContainer.leftPadding(), point.y(), locationInContainer.rightPadding() + locationInContainer.leftPadding() + 1, 1));
 
-    if (!anyLineIntersectsRect(layoutObject, rect, accumulatedOffset))
+    if (!anyLineIntersectsRect(layoutObject, rect, accumulatedOffset)) {
+        InlineFlowBox* first = firstLineBox();
+        RootInlineBox& firstRoot = first->root();
+        InlineFlowBox* last = lastLineBox();
+        RootInlineBox& lastRoot = last->root();
+
+        result.shrinkValidityRect(first->visualOverflowRect(firstRoot.lineTop(), firstRoot.lineBottom()));
+        if (first != last)
+            result.shrinkValidityRect(last->visualOverflowRect(lastRoot.lineTop(), lastRoot.lineBottom()));
         return false;
+    }
 
     // See if our root lines contain the point.  If so, then we hit test
     // them further.  Note that boxes can easily overlap, so we can't make any assumptions
     // based off positions of our first line box or our last line box.
     for (InlineFlowBox* curr = lastLineBox(); curr; curr = curr->prevLineBox()) {
         RootInlineBox& root = curr->root();
         if (rangeIntersectsRect(layoutObject, curr->logicalTopVisualOverflow(root.lineTop()), curr->logicalBottomVisualOverflow(root.lineBottom()), rect, accumulatedOffset)) {
             bool inside = curr->nodeAtPoint(result, locationInContainer, accumulatedOffset, root.lineTop(), root.lineBottom());
             if (inside) {
-                layoutObject->updateHitTestResult(result, locationInContainer.point() - toLayoutSize(accumulatedOffset));
+                layoutObject->updateHitTestResult(result, locationInContainer.point() - toLayoutSize(accumulatedOffset), curr->visualOverflowRect(root.lineTop(), root.lineBottom()));
                 return true;
             }
+        } else {
+            result.shrinkValidityRect(curr->visualOverflowRect(root.lineTop(), root.lineBottom()));
         }
     }
 
     return false;
 }
 
 void LineBoxList::dirtyLinesFromChangedChild(LayoutObject* container, LayoutObject* child)
 {
     if (!container->parent() || (container->isLayoutBlock() && (container->selfNeedsLayout() || !container->isLayoutBlockFlow())))
         return;
@@ skipping 84 matching lines @@
         ASSERT(child->prevLineBox() == prev);
         prev = child;
     }
     ASSERT(prev == m_lastLineBox);
 #endif
 }
 
 #endif
 
 }