[WIP] Add WebCore.UseCounter UMA to supercede FeatureObserver

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

Index: third_party/WebKit/Source/core/frame/UseCounter.h
diff --git a/third_party/WebKit/Source/core/frame/UseCounter.h b/third_party/WebKit/Source/core/frame/UseCounter.h
index a05f092d92800c6e30de69e1c9708dbe680a1fab..95b754dfff1d9e131dd8fa8e4f73481b33f8136b 100644
--- a/third_party/WebKit/Source/core/frame/UseCounter.h
+++ b/third_party/WebKit/Source/core/frame/UseCounter.h
@@ -60,8 +60,10 @@ class CORE_EXPORT UseCounter {
     DISALLOW_NEW();
     WTF_MAKE_NONCOPYABLE(UseCounter);
 public:
-    UseCounter();
-    ~UseCounter();
+    UseCounter()
+        : m_featuresReported(NumberOfFeatures)
+        , m_CSSFeaturesReported(lastUnresolvedCSSProperty + 1)
+    {}
 
     enum Feature {
         // Do not change assigned numbers of existing items: add new features
@@ -1237,58 +1239,44 @@ public:
     bool isCounted(CSSPropertyID unresolvedProperty);
 
     void didCommitLoad();
+    void deprecatedDidCommitFrameLoad() { m_legacyCounter.updateMeasurements(); }
+
+    void recordMeasurement(Feature);
+    bool hasRecordedMeasurement(Feature feature) const { return m_featuresReported.quickGet(feature); }

[dtapuska, 2016/05/31 01:10:51]

The semantics of this are changing wrt muted count. 

 
     static UseCounter* getFrom(const Document*);
     static UseCounter* getFrom(const CSSStyleSheet*);
     static UseCounter* getFrom(const StyleSheetContents*);
 
-    static int mapCSSPropertyIdToCSSSampleIdForHistogram(int id);
+    static int mapCSSPropertyIdToCSSSampleIdForHistogram(CSSPropertyID);
 
     static void muteForInspector();
     static void unmuteForInspector();
+    static bool isMuted() { return m_muteCount; }
 
-    void recordMeasurement(Feature feature) { m_countBits.recordMeasurement(feature); }
-    void updateMeasurements();
+protected:
+    BitVector m_featuresReported;
+    BitVector m_CSSFeaturesReported;
 
-    bool hasRecordedMeasurement(Feature feature) const { return m_countBits.hasRecordedMeasurement(feature); }
+    friend class UseCounterTest;
+    static int m_muteCount;
 
-    class CountBits {
-        DISALLOW_NEW();
+private:
+    // Encapsulates the work to preserve the old "FeatureObserver" histogram with original (buggy)
+    // semantics.  Will be removed eventually.  http://crbug.com/597963
+    class LegacyCounter {
     public:
-        CountBits() : m_bits(NumberOfFeatures) { }
-
-        bool hasRecordedMeasurement(Feature feature) const
-        {
-            if (UseCounter::m_muteCount)
-                return false;
-            ASSERT(feature != PageDestruction); // PageDestruction is reserved as a scaling factor.
-            ASSERT(feature < NumberOfFeatures);
-
-            return m_bits.quickGet(feature);
-        }
-
-        void recordMeasurement(Feature feature)
-        {
-            if (UseCounter::m_muteCount)
-                return;
-            ASSERT(feature != PageDestruction); // PageDestruction is reserved as a scaling factor.
-            ASSERT(feature < NumberOfFeatures);
-
-            m_bits.quickSet(feature);
-        }
-
+        LegacyCounter();
+        ~LegacyCounter();
+        void recordMeasurement(Feature);
         void updateMeasurements();
+        bool hasRecordedMeasurement(Feature) const;

[dtapuska, 2016/05/31 01:10:51]

Is this method called anywhere?

+        void countCSS(CSSPropertyID feature);

[dtapuska, 2016/05/31 01:10:51]

Likely using a consistent verbage here is good. Count vs record. It is different
for features vs css. 

 
     private:
-        BitVector m_bits;
-    };
-
-protected:
-    friend class UseCounterTest;
-    static int m_muteCount;
-
-    CountBits m_countBits;
-    BitVector m_CSSFeatureBits;
+        BitVector m_countBits;
+        BitVector m_CSSFeatureBits;
+    } m_legacyCounter;
 };
 
 } // namespace blink