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..e6177fb07d71af5aaa46d8e7ad7499929d52f648 100644
--- a/chrome/browser/io_thread.h
+++ b/chrome/browser/io_thread.h
@@ -598,6 +598,10 @@ 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);