[Sync] Store the past 10 traffic records in memory.

sync/sessions/sync_session_context.h

Index: sync/sessions/sync_session_context.h
diff --git a/sync/sessions/sync_session_context.h b/sync/sessions/sync_session_context.h
index 94129ce9cee033d9b0815e1056b514852f9ece22..60e3d597670855dcc85448dea844598c264d424f 100644
--- a/sync/sessions/sync_session_context.h
+++ b/sync/sessions/sync_session_context.h
@@ -27,6 +27,7 @@
 #include "base/time.h"
 #include "sync/engine/model_safe_worker.h"
 #include "sync/engine/syncer_types.h"
+#include "sync/engine/traffic_recorder.h"
 #include "sync/sessions/debug_info_getter.h"
 
 namespace syncable {
@@ -123,6 +124,10 @@ class SyncSessionContext {
   // new throttled types this will remain constant through out the sync cycle.
   syncable::ModelTypeSet GetThrottledTypes() const;
 
+  browser_sync::TrafficRecorder* traffic_recorder() {
+    return &traffic_recorder_;
+  }
+
  private:
   typedef std::map<syncable::ModelType, base::TimeTicks> UnthrottleTimes;
 
@@ -177,6 +182,9 @@ class SyncSessionContext {
   // unthrottled.
   UnthrottleTimes unthrottle_times_;
 
+  // TODO(lipalani): Move the creation of this to |SyncManager|.
+  browser_sync::TrafficRecorder traffic_recorder_;
+
   DISALLOW_COPY_AND_ASSIGN(SyncSessionContext);
 };