Add histograms to track synced pref changes.

chrome/browser/prefs/pref_metrics_service.h

Index: chrome/browser/prefs/pref_metrics_service.h
diff --git a/chrome/browser/prefs/pref_metrics_service.h b/chrome/browser/prefs/pref_metrics_service.h
index 647cd9497653d1e5cb10be47452ccf45fccd051f..fc48935c9f9f484917598ebee4b4ac1c33f691d6 100644
--- a/chrome/browser/prefs/pref_metrics_service.h
+++ b/chrome/browser/prefs/pref_metrics_service.h
@@ -5,7 +5,12 @@
 #ifndef CHROME_BROWSER_PREFS_PREF_METRICS_SERVICE_H_
 #define CHROME_BROWSER_PREFS_PREF_METRICS_SERVICE_H_
 
+#include <map>
+#include <string>
+
+#include "base/memory/scoped_ptr.h"
 #include "base/memory/singleton.h"
+#include "chrome/browser/prefs/synced_pref_change_registrar.h"
 #include "chrome/browser/profiles/profile.h"
 #include "components/browser_context_keyed_service/browser_context_keyed_service.h"
 #include "components/browser_context_keyed_service/browser_context_keyed_service_factory.h"
@@ -34,11 +39,51 @@ class PrefMetricsService : public BrowserContextKeyedService {
     virtual content::BrowserContext* GetBrowserContextToUse(
         content::BrowserContext* context) const OVERRIDE;
   };
+
  private:
+  // Use a map to convert domains to their histogram identifiers. Ids are
+  // defined in tools/metrics/histograms/histograms.xml and (usually) also in
+  // chrome/browser/search_engines/prepopulated_engines.json.
+  typedef std::map<std::string, int> DomainIdMap;
+
+  // Function to log a Value to a histogram
+  typedef base::Callback<void(const std::string&, const Value*)>
+      LogHistogramValueCallback;
+
   // Record prefs state on browser context creation.
   void RecordLaunchPrefs();
 
+  // Register callbacks for synced pref changes.
+  void RegisterSyncedPrefObservers();
+
+  // Registers a histogram logging callback for a synced pref change.
+  void AddPrefObserver(const std::string& path,
+                       const std::string& histogram_name_prefix,
+                       const LogHistogramValueCallback& callback);
+
+  // Generic callback to observe a synced pref change.
+  void OnPrefChanged(const std::string& histogram_name_prefix,
+                     const LogHistogramValueCallback& callback,
+                     const std::string& path,
+                     bool from_sync);
+
+  // Callback for a boolean pref change histogram.
+  void LogBooleanPrefChange(const std::string& histogram_name,
+                            const Value* value);
+
+  // Callback for an integer pref change histogram.
+  void LogIntegerPrefChange(int boundary_value,
+                            const std::string& histogram_name,
+                            const Value* value);
+
+  // Callback for a list pref change. Each item in the list
+  // is logged using the given histogram callback.
+  void LogListPrefChange(const LogHistogramValueCallback& item_callback,
+                         const std::string& histogram_name,
+                         const Value* value);
+
   Profile* profile_;
+  scoped_ptr<SyncedPrefChangeRegistrar> synced_pref_change_registrar_;
 };
 
 #endif  // CHROME_BROWSER_PREFS_PREF_METRICS_SERVICE_H_