[blink] Remove Event.HitTest metric.

This metric has expired.

Fixed: 1072662
Change-Id: Iad422fcd3ba65a8e43da385961aaac406c5e2d4e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2524921Reviewed-by: Dave Tapuska <dtapuska@chromium.org>
Reviewed-by: Steven Holte <holte@chromium.org>
Commit-Queue: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#825490}

third_party/blink/renderer/core/layout/hit_test_cache.cc

@@ -5,7 +5,6 @@
 #include "third_party/blink/renderer/core/layout/hit_test_cache.h"
 
 #include "third_party/blink/public/platform/platform.h"
-#include "third_party/blink/renderer/platform/instrumentation/histogram.h"
 
 namespace blink {
 
@@ -13,9 +12,7 @@ bool HitTestCache::LookupCachedResult(const HitTestLocation& location,
                                       HitTestResult& hit_result,
                                       uint64_t dom_tree_version) {
   bool result = false;
-  HitHistogramMetric metric = HitHistogramMetric::MISS;
   if (hit_result.GetHitTestRequest().AvoidCache()) {
-    metric = HitHistogramMetric::MISS_EXPLICIT_AVOID;
     // For now we don't support rect based hit results.
   } else if (dom_tree_version == dom_tree_version_ &&
              !location.IsRectBasedTest()) {
@@ -23,20 +20,13 @@ bool HitTestCache::LookupCachedResult(const HitTestLocation& location,
       if (cached_item.location.Point() == location.Point()) {
         if (hit_result.GetHitTestRequest().EqualForCacheability(
                 cached_item.result.GetHitTestRequest())) {
-          metric = HitHistogramMetric::HIT_EXACT_MATCH;
           result = true;
           hit_result = cached_item.result;
           break;
         }
-        metric = HitHistogramMetric::MISS_VALIDITY_RECT_MATCHES;
       }
     }
   }
-  DEFINE_STATIC_LOCAL(
-      EnumerationHistogram, hit_test_histogram,
-      ("Event.HitTest",
-       static_cast<int32_t>(HitHistogramMetric::MAX_HIT_METRIC)));
-  hit_test_histogram.Count(static_cast<int32_t>(metric));
   return result;
 }
 

third_party/blink/renderer/core/layout/hit_test_cache.h

@@ -65,22 +65,6 @@ class CORE_EXPORT HitTestCache final : public GarbageCollected<HitTestCache> {
   void Trace(Visitor*) const;
 
  private:
-  // 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,
-  };
-
   unsigned update_index_;
 
   HeapVector<HitTestCacheEntry, HIT_TEST_CACHE_SIZE> items_;

tools/metrics/histograms/histograms_xml/event/histograms.xml

@@ -182,6 +182,9 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="Event.HitTest" enum="EventHitTest" expires_after="2020-05-31">
+  <obsolete>
+    Removed in M88.
+  </obsolete>
   <owner>dtapuska@chromium.org</owner>
   <summary>
     For each hit test, records whether it was a hit or miss, and why.