Add external data use observer

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 5ef542fb8b2312b9cfe45a1a50ae0b08179a284c..4586bb6f76486164d3eb96ff1d871ed534cc8552 100644
--- a/chrome/browser/io_thread.h
+++ b/chrome/browser/io_thread.h
@@ -20,6 +20,7 @@
 #include "base/time/time.h"
 #include "chrome/browser/net/chrome_network_delegate.h"
 #include "chrome/browser/net/ssl_config_service_manager.h"
+#include "components/data_usage/core/data_use_aggregator.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/browser_thread_delegate.h"
 #include "net/base/network_change_notifier.h"
@@ -43,10 +44,6 @@ namespace extensions {
 class EventRouterForwarder;
 }
 
-namespace data_usage {
-class DataUseAggregator;
-}
-
 namespace net {
 class CertPolicyEnforcer;
 class CertVerifier;
@@ -126,9 +123,6 @@ class IOThread : public content::BrowserThreadDelegate {
     Globals();
     ~Globals();
 
-    // Global aggregator of data use. It must outlive the
-    // |system_network_delegate|.
-    scoped_ptr<data_usage::DataUseAggregator> data_use_aggregator;
     // The "system" NetworkDelegate, used for Profile-agnostic network events.
     scoped_ptr<net::NetworkDelegate> system_network_delegate;
     scoped_ptr<net::HostResolver> host_resolver;
@@ -252,6 +246,8 @@ class IOThread : public content::BrowserThreadDelegate {
 
   base::TimeTicks creation_time() const;
 
+  data_usage::DataUseAggregator* data_use_aggregator() const;
+
   // Returns true if QUIC should be enabled for data reduction proxy, either as
   // a result of a field trial or a command line flag.
   static bool ShouldEnableQuicForDataReductionProxy();
@@ -513,6 +509,13 @@ class IOThread : public content::BrowserThreadDelegate {
   // True if QUIC is allowed by policy.
   bool is_quic_allowed_by_policy_;
 
+  // Global aggregator of data use. It must outlive the
+  // |system_network_delegate|.
+  scoped_ptr<data_usage::DataUseAggregator> data_use_aggregator_;
+  // An external observer of data use.
+  scoped_ptr<data_usage::DataUseAggregator::Observer>
+      external_data_use_observer_;
+
   const base::TimeTicks creation_time_;
 
   base::WeakPtrFactory<IOThread> weak_factory_;