Implement a Hit Test Cache.

LayoutTests/fast/events/hit-test-cache-expected.txt

Index: LayoutTests/fast/events/hit-test-cache-expected.txt
diff --git a/LayoutTests/fast/events/hit-test-cache-expected.txt b/LayoutTests/fast/events/hit-test-cache-expected.txt
new file mode 100644
index 0000000000000000000000000000000000000000..ca942311ea9e1b6487962b3a76251c86e98c21ad
--- /dev/null
+++ b/LayoutTests/fast/events/hit-test-cache-expected.txt
@@ -0,0 +1,28 @@
+Ensure hit test cache works in correct scenarios of scrolling, dom and style changes.
+
+On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
+
+
+PASS successfullyParsed is true
+
+TEST COMPLETE
+Hit test fixed div after scroll
+---------------------
+Element is DIV, target
+Element (no cache) is DIV, target
+Hit Test 2/0
+Element is DIV, testArea
+Element (no cache) is DIV, testArea
+Hit Test 2/0
+Element is DIV, target
+Element (no cache) is DIV, target
+Hit Test 2/0
+Hit test after style change
+---------------------
+Element is DIV, target
+Element (no cache) is DIV, target
+Hit Test 2/0
+Element is DIV, target
+Element (no cache) is DIV, target
+Hit Test 2/0
+