Implement a Hit Test Cache.

Source/core/layout/line/LineBoxList.cpp

Index: Source/core/layout/line/LineBoxList.cpp
diff --git a/Source/core/layout/line/LineBoxList.cpp b/Source/core/layout/line/LineBoxList.cpp
index 4f391d5a96c5bec31fc48c130183cf14b4e0896a..e293a2d9d7890e1eccff47dcad2abebd975c2b47 100644
--- a/Source/core/layout/line/LineBoxList.cpp
+++ b/Source/core/layout/line/LineBoxList.cpp
@@ -209,8 +209,17 @@ bool LineBoxList::hitTest(LayoutBoxModelObject* layoutObject, HitTestResult& res
         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
@@ -220,9 +229,11 @@ bool LineBoxList::hitTest(LayoutBoxModelObject* layoutObject, HitTestResult& res
         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()));
         }
     }