Added trace events for blink feature usage

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 18 matching lines @@
 #include "core/css/StyleSheetContents.h"
 #include "core/dom/Document.h"
 #include "core/dom/ExecutionContext.h"
 #include "core/frame/Deprecation.h"
 #include "core/frame/FrameConsole.h"
 #include "core/frame/FrameHost.h"
 #include "core/frame/LocalFrame.h"
 #include "core/inspector/ConsoleMessage.h"
 #include "core/workers/WorkerGlobalScope.h"
 #include "platform/Histogram.h"
+#include "platform/TraceEvent.h"
 
 namespace blink {
 
 static int totalPagesMeasuredCSSSampleId() { return 1; }
 
 int UseCounter::mapCSSPropertyIdToCSSSampleIdForHistogram(int id)
 {
     CSSPropertyID cssPropertyID = static_cast<CSSPropertyID>(id);
 
     switch (cssPropertyID) {
@@ skipping 606 matching lines @@
 }
 
 void UseCounter::count(const Frame* frame, Feature feature)
 {
     if (!frame)
         return;
     FrameHost* host = frame->host();
     if (!host)
         return;
 
-    ASSERT(Deprecation::deprecationMessage(feature).isEmpty());
-    host->useCounter().recordMeasurement(feature);
+    host->useCounter().count(feature);
 }
 
 void UseCounter::count(const Document& document, Feature feature)
 {
     count(document.frame(), feature);
 }
 
 bool UseCounter::isCounted(Document& document, Feature feature)
 {
     Frame* frame = document.frame();
@@ skipping 67 matching lines @@
 }
 
 void UseCounter::count(CSSParserMode cssParserMode, CSSPropertyID feature)
 {
     ASSERT(feature >= firstCSSProperty);
     ASSERT(feature <= lastUnresolvedCSSProperty);
 
     if (!isUseCounterEnabledForMode(cssParserMode) || m_muteCount)
         return;
 
+    TRACE_EVENT1(TRACE_DISABLED_BY_DEFAULT("blink.feature_usage"), "CSSFeatureUsed", "feature", feature);
     m_CSSFeatureBits.quickSet(feature);
 }
 
 void UseCounter::count(Feature feature)
 {
     ASSERT(Deprecation::deprecationMessage(feature).isEmpty());
+    TRACE_EVENT1(TRACE_DISABLED_BY_DEFAULT("blink.feature_usage"), "FeatureUsed", "feature", feature);

[foolip, 2016/08/03 14:53:27]

This relates to
https://codereview.chromium.org/2203913002/diff/1/third_party/WebKit/Source/c...

Deprecation::countDeprecation doesn't use this code path, so it looks like
deprecated things will be missed here. And it first checks
hasRecordedMeasurement(feature) to avoid double logging to the console, so some
care is needed to not just trace once for deprecations but any number of times
for the rest.

What happens if you try to push down the tracing into
UseCounter::recordMeasurement inside the m_muteCount guard and also check
hasRecordedMeasurement there?

Something like that would be a closer fit for the above change, where you trace
after some guards and right before the poking and the bit vector.

[Pat Meenan, 2016/08/03 18:43:25]

Done.

     recordMeasurement(feature);
 }
 
 UseCounter* UseCounter::getFrom(const Document* document)
 {
     if (document && document->frameHost())
         return &document->frameHost()->useCounter();
     return 0;
 }
 
 UseCounter* UseCounter::getFrom(const CSSStyleSheet* sheet)
 {
     if (sheet)
         return getFrom(sheet->contents());
     return 0;
 }
 
 UseCounter* UseCounter::getFrom(const StyleSheetContents* sheetContents)
 {
     // FIXME: We may want to handle stylesheets that have multiple owners
     //        https://crbug.com/242125
     if (sheetContents && sheetContents->hasSingleOwnerNode())
         return getFrom(sheetContents->singleOwnerDocument());
     return 0;
 }
 
 } // namespace blink