Enable HitTestCache by default.

Source/core/layout/HitTestCache.h

Index: Source/core/layout/HitTestCache.h
diff --git a/Source/core/layout/HitTestCache.h b/Source/core/layout/HitTestCache.h
index 1139450ed1e166eb73a64e78466781ca41bd6ad1..2aa787f109eec1628804020e3c922af44cf2c478 100644
--- a/Source/core/layout/HitTestCache.h
+++ b/Source/core/layout/HitTestCache.h
@@ -46,10 +46,6 @@ public:
 
     void clear();
 
-    // Verify that the |actual| object matches the |expected| object; and
-    // log UMA metrics indicating the result.
-    static void verifyCachedResult(const HitTestResult& expected, const HitTestResult& actual);
-
     // Adds a HitTestResult to the cache.
     void addCachedResult(const HitTestResult&, uint64_t domTreeVersion);
 
@@ -76,19 +72,6 @@ private:
         MAX_HIT_METRIC = HIT_REGION_MATCH,
     };
 
-    // These values are reported in UMA as the "EventHitTestValidity"
-    // enumeration. Do not reorder, append new values at the end,
-    // deprecate old values and update histograms.xml.
-    enum class ValidityHistogramMetric {
-        VALID_EXACT_MATCH, // Correct node for exact point test.
-        VALID_REGION, // Correct node for region check.
-        INCORRECT_RECT_BASED_EXACT_MATCH, // Wrong node returned for cache hit with point was exact match and rect based test.
-        INCORRECT_POINT_EXACT_MATCH, // Wrong node returned for cache hit with exact point match and was explicit point test.
-        INCORRECT_RECT_BASED_REGION, // Wrong node returned for rect with region matching and was rect based test.
-        INCORRECT_POINT_REGION, // Wrong node returned for point with region matching and was explicit point test.
-        MAX_VALIDITY_METRIC = INCORRECT_POINT_REGION,
-    };
-
     unsigned m_updateIndex;
     WillBeHeapVector<HitTestResult, HIT_TEST_CACHE_SIZE> m_items;
     uint64_t m_domTreeVersion;