Implement UMA log throttling for cellular connections

chrome/browser/io_thread.h

Index: chrome/browser/io_thread.h
diff --git a/chrome/browser/io_thread.h b/chrome/browser/io_thread.h
index fc27d9b337cfbd860cba165afa4e4088108874c7..7293dd591e4c0b7a60de739bc748cc576f2becb5 100644
--- a/chrome/browser/io_thread.h
+++ b/chrome/browser/io_thread.h
@@ -290,6 +290,9 @@ class IOThread : public content::BrowserThreadDelegate {
   // a result of a field trial or a command line flag.
   static bool ShouldEnableQuicForDataReductionProxy();
 
+  // Returns the callback for updating data use prefs.
+  const metrics::UpdateUsagePrefCallbackType& GetMetricsDataUseForwarder();
+
  private:
   // Map from name to value for all parameters associate with a field trial.
   typedef std::map<std::string, std::string> VariationParameters;
@@ -598,6 +601,10 @@ class IOThread : public content::BrowserThreadDelegate {
 
   const base::TimeTicks creation_time_;
 
+  // Callback for updating data use prefs which needs to be initialized on UI
+  // thread and passed to |ChromeNetworkDelegate|.
+  metrics::UpdateUsagePrefCallbackType metrics_data_use_forwarder_;
+
   base::WeakPtrFactory<IOThread> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(IOThread);