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..97180c4401aa7cfd67fab8a1a0976ab71849bf2b 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;
@@ -129,6 +126,9 @@ class IOThread : public content::BrowserThreadDelegate {
     // 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;

[mmenke, 2015/10/12 16:59:26]

Actually, can this just be in IOThread?  If you need these to have one of the
properties of globals (Settable for testing, used in InitFromGlobals, exposed
publicly), that's fine, though I'd like to know which one it is.

[tbansal1, 2015/10/12 17:05:18]

No, I do not think I need any of those properties. It seems that
|data_use_aggregator| can also move to IOThread? I just wanted to keep them
together. wdyt?

[tbansal1, 2015/10/12 22:39:14]

Done.

[tbansal1, 2015/10/12 22:39:14]

Done.

     // The "system" NetworkDelegate, used for Profile-agnostic network events.
     scoped_ptr<net::NetworkDelegate> system_network_delegate;
     scoped_ptr<net::HostResolver> host_resolver;