Factor out dependncy on download throttling from core download code.

chrome/browser/browser_process_impl.h

Index: chrome/browser/browser_process_impl.h
===================================================================
--- chrome/browser/browser_process_impl.h	(revision 96872)
+++ chrome/browser/browser_process_impl.h	(working copy)
@@ -97,6 +97,7 @@
   virtual const std::string& GetApplicationLocale();
   virtual void SetApplicationLocale(const std::string& locale);
   virtual DownloadStatusUpdater* download_status_updater();
+  virtual DownloadRequestLimiter* download_request_limiter();
   virtual TabCloseableStateWatcher* tab_closeable_state_watcher();
   virtual BackgroundModeManager* background_mode_manager();
   virtual StatusTray* status_tray();
@@ -282,6 +283,8 @@
   // so we don't have to worry about lazy initialization.
   DownloadStatusUpdater download_status_updater_;
 
+  scoped_refptr<DownloadRequestLimiter> download_request_limiter_;
+
   // Ensures that the observers of plugin/print disable/enable state
   // notifications are properly added and removed.
   PrefChangeRegistrar pref_change_registrar_;