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());

[foolip, 2016/08/08 19:59:11]

This ASSERT should still hold, right, or why was it removed?

[Pat Meenan, 2016/08/09 19:06:32]

UseCounter::count() is exactly this assert + the recordMeasurement() call. 
Instead of duplicating both of them I changed it to pass through to the count()
entry point and leave the logic there.

This isn't necessary for my change since I moved the tracing into the deeper
recordMeasurement() call anyway but came out as part of the cleanup from earlier
iterations.

[foolip, 2016/08/11 08:03:44]

Acknowledged.

-    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());
     recordMeasurement(feature);
 }
 
 UseCounter* UseCounter::getFrom(const Document* document)
@@ skipping 12 matching lines @@
 
 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;
 }
 
+void UseCounter::recordMeasurement(Feature feature)
+{
+    if (!m_muteCount) {

[foolip, 2016/08/08 19:59:11]

Can you do an early return instead, and put this somewhere around
unmuteForInspector/updateMeasurements to be closer to the header file's order?

[Pat Meenan, 2016/08/09 19:06:32]

Done.

+        m_countBits.recordMeasurement(feature);
+        TRACE_EVENT1(TRACE_DISABLED_BY_DEFAULT("blink.feature_usage"), "FeatureUsed", "feature", feature);
+    }
+}
+
 } // namespace blink