Enable HitTestCache by default.

Source/core/layout/HitTestCache.h

 // Copyright (c) 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef HitTestCache_h
 #define HitTestCache_h
 
 #include "core/CoreExport.h"
 #include "core/layout/HitTestResult.h"
 #include "platform/heap/Handle.h"
@@ skipping 28 matching lines @@
     {
         return adoptPtrWillBeNoop(new HitTestCache);
     }
 
     // Check the cache for a possible hit and update |result| if
     // hit encountered; returning true. Otherwise false.
     bool lookupCachedResult(HitTestResult&, uint64_t domTreeVersion);
 
     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);
 
     DECLARE_TRACE();
 
 private:
     HitTestCache()
         : m_updateIndex(0)
         , m_domTreeVersion(0) { }
 
     // The below UMA values reference a validity region. This code has not
     // been written yet; and exact matches are only supported but the
     // UMA enumerations have been added for future support.
 
     // These values are reported in UMA as the "EventHitTest" enumeration.
     // Do not reorder, append new values at the end, deprecate old
     // values and update histograms.xml.
     enum class HitHistogramMetric {
         MISS, // Miss, not found in cache.
         MISS_EXPLICIT_AVOID, // Miss, callee asked to explicitly avoid cache.
         MISS_VALIDITY_RECT_MATCHES, // Miss, validity region matches, type doesn't.
         HIT_EXACT_MATCH, // Hit, exact point matches.
         HIT_REGION_MATCH, // Hit, validity region matches.
         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;
 };
 
 } // namespace blink
 
 #endif // HitTestCache_h