UseCounter: Introduce UseCounter::Observer for layout tests

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

Index: third_party/WebKit/Source/core/frame/UseCounter.cpp
diff --git a/third_party/WebKit/Source/core/frame/UseCounter.cpp b/third_party/WebKit/Source/core/frame/UseCounter.cpp
index f424c1430b58935699917abd1a4a054bb88f957c..d020ed4ef09f2fd7668c0ef77ea680aa9500eb66 100644
--- a/third_party/WebKit/Source/core/frame/UseCounter.cpp
+++ b/third_party/WebKit/Source/core/frame/UseCounter.cpp
@@ -1125,6 +1125,7 @@ void UseCounter::recordMeasurement(Feature feature) {
       TRACE_EVENT1(TRACE_DISABLED_BY_DEFAULT("blink.feature_usage"),
                    "FeatureFirstUsed", "feature", feature);
       featuresHistogram().count(feature);
+      notifyFeatureCounted(feature);
     }
     m_featuresRecorded.quickSet(feature);
   }
@@ -1143,6 +1144,10 @@ bool UseCounter::hasRecordedMeasurement(Feature feature) const {
   return m_featuresRecorded.quickGet(feature);
 }
 
+DEFINE_TRACE(UseCounter) {
+  visitor->trace(m_observers);
+}
+
 void UseCounter::didCommitLoad(KURL url) {
   m_legacyCounter.updateMeasurements();
 
@@ -1193,6 +1198,16 @@ 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)
@@ -1249,6 +1264,17 @@ 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