Adding UseCounter specific for extensions

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 88f37a8c0dc938d087a2103a172eb01a2aa1dca8..6a06d43f06372e76ee61daacfae2c38df7798ce0 100644
--- a/third_party/WebKit/Source/core/frame/UseCounter.h
+++ b/third_party/WebKit/Source/core/frame/UseCounter.h
@@ -67,7 +67,12 @@ class CORE_EXPORT UseCounter {
   enum Context {
     kDefaultContext,
     // Counters for SVGImages (lifetime independent from other pages).
-    kSVGImageContext
+    kSVGImageContext,
+    // Counters for extensions.
+    kExtensionContext,
+    // Context when counters should be disabled (eg, internal pages such as
+    // about, chrome-devtools, etc).
+    kDisabledContext
   };
 
   UseCounter(Context = kDefaultContext);
@@ -1587,8 +1592,8 @@ class CORE_EXPORT UseCounter {
   };
 
   // An interface to observe UseCounter changes. Note that this is never
-  // notified when the counter is disabled by |m_muteCount| or
-  // |m_disableReporting|.
+  // notified when the counter is disabled by |m_muteCount| or when |m_context|
+  // is DisabledContext.
   class Observer : public GarbageCollected<Observer> {
    public:
     // Notified when a feature is counted for the first time. This should return
@@ -1650,8 +1655,8 @@ class CORE_EXPORT UseCounter {
 
  private:
   // Notifies that a feature is newly counted to |m_observers|. This shouldn't
-  // be called when the counter is disabled by |m_muteCount| or
-  // |m_disableReporting|.
+  // be called when the counter is disabled by |m_muteCount| or when |m_context|
+  // if DisabledContext.
   void NotifyFeatureCounted(Feature);
 
   EnumerationHistogram& FeaturesHistogram() const;
@@ -1661,10 +1666,8 @@ class CORE_EXPORT UseCounter {
   // If non-zero, ignore all 'count' calls completely.
   unsigned mute_count_;
 
-  // If true, disable reporting all histogram entries.
-  bool disable_reporting_;
-
-  // The scope represented by this UseCounter instance.
+  // The scope represented by this UseCounter instance, which must be fixed for
+  // the duration of a page but can change when a new page is loaded.
   Context context_;
 
   // Track what features/properties have been reported to the (non-legacy)