UseCounter: Introduce UseCounter::Observer for layout tests

third_party/WebKit/Source/core/frame/UseCounter.cpp

 /*
  * Copyright (C) 2012 Google, Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 1107 matching lines @@
              PageVisits);  // PageDestruction is reserved as a scaling factor.
   DCHECK(feature < NumberOfFeatures);
 
   if (!m_featuresRecorded.quickGet(feature)) {
     // Note that HTTPArchive tooling looks specifically for this event - see
     // https://github.com/HTTPArchive/httparchive/issues/59
     if (!m_disableReporting) {
       TRACE_EVENT1(TRACE_DISABLED_BY_DEFAULT("blink.feature_usage"),
                    "FeatureFirstUsed", "feature", feature);
       featuresHistogram().count(feature);
+      notifyFeatureCounted(feature);
     }
     m_featuresRecorded.quickSet(feature);
   }
   m_legacyCounter.countFeature(feature);
 }
 
 bool UseCounter::hasRecordedMeasurement(Feature feature) const {
   if (m_muteCount)
     return false;
 
   DCHECK(feature != OBSOLETE_PageDestruction &&
          feature !=
              PageVisits);  // PageDestruction is reserved as a scaling factor.
   DCHECK(feature < NumberOfFeatures);
 
   return m_featuresRecorded.quickGet(feature);
 }
 
+DEFINE_TRACE(UseCounter) {
+  visitor->trace(m_observers);
+}
+
 void UseCounter::didCommitLoad(KURL url) {
   m_legacyCounter.updateMeasurements();
 
   // Reset state from previous load.
   m_disableReporting = false;
 
   // Use the protocol of the document being loaded into the main frame to
   // decide whether this page is interesting from a metrics perspective.
   // Note that SVGImage cases always have an about:blank URL
   if (m_context == DefaultContext &&
@@ skipping 30 matching lines @@
   FrameHost* host = frame->host();
   if (!host)
     return false;
   return host->useCounter().hasRecordedMeasurement(feature);
 }
 
 bool UseCounter::isCounted(CSSPropertyID unresolvedProperty) {
   return m_CSSRecorded.quickGet(unresolvedProperty);
 }
 
+void UseCounter::addObserver(Document& document, Observer* observer) {

[Rick Byers, 2017/02/13 20:46:31]

nit: IMHO this would make more sense as an instance method on UseCounter instead
of a static method.  We have a few static helper methods to factor out some
biolerplate for the really common cases, but this is something that's only going
to be used in one or two places so I wouldn't both with a static personally.

This is minor though - if there's a reason you prefer this to be static then
feel free to leave it.

[nhiroki, 2017/02/14 02:03:29]

There is no special reason. I just aligned it with other helpers when I made an
initial patch. I agree that an instance method makes more sense. Done.

+  Frame* frame = document.frame();
+  if (!frame)
+    return;
+  FrameHost* host = frame->host();
+  if (!host)
+    return;
+  host->useCounter().m_observers.insert(observer);
+}
+
 bool UseCounter::isCounted(Document& document, const String& string) {
   Frame* frame = document.frame();
   if (!frame)
     return false;
   FrameHost* host = frame->host();
   if (!host)
     return false;
 
   CSSPropertyID unresolvedProperty = unresolvedCSSPropertyID(string);
   if (unresolvedProperty == CSSPropertyInvalid)
@@ skipping 36 matching lines @@
     }
     m_CSSRecorded.quickSet(property);
   }
   m_legacyCounter.countCSS(property);
 }
 
 void UseCounter::count(Feature feature) {
   recordMeasurement(feature);
 }
 
+void UseCounter::notifyFeatureCounted(Feature feature) {
+  DCHECK(!m_muteCount);
+  DCHECK(!m_disableReporting);
+  HeapHashSet<Member<Observer>> toBeRemoved;
+  for (auto observer : m_observers) {
+    if (observer->onCountFeature(feature))
+      toBeRemoved.insert(observer);
+  }
+  m_observers.removeAll(toBeRemoved);
+}
+
 EnumerationHistogram& UseCounter::featuresHistogram() const {
   // Every SVGImage has it's own Page instance, and multiple web pages can
   // share the usage of a single SVGImage.  Ideally perhaps we'd delegate
   // metrics from an SVGImage to one of the Page's it's displayed in, but
   // that's tricky (SVGImage is intentionally isolated, and the Page that
   // created it may not even exist anymore).
   // So instead we just use a dedicated histogram for the SVG case.
   DEFINE_STATIC_LOCAL(
       blink::EnumerationHistogram, histogram,
       ("Blink.UseCounter.Features", blink::UseCounter::NumberOfFeatures));
@@ skipping 73 matching lines @@
     }
   }
 
   if (needsPagesMeasuredUpdate)
     cssPropertiesHistogram.count(totalPagesMeasuredCSSSampleId());
 
   m_CSSBits.clearAll();
 }
 
 }  // namespace blink