Add histograms for network activity, and total/cumulative

net/http/http_transaction_delegate.h

Index: net/http/http_transaction_delegate.h
===================================================================
--- net/http/http_transaction_delegate.h	(revision 150909)
+++ net/http/http_transaction_delegate.h	(working copy)
@@ -7,15 +7,18 @@
 
 namespace net {
 
-// Delegate class receiving notifications when cache actions start and finish,
-// i.e. when the object starts and finishes waiting on an underlying cache.
-// The owner of a HttpTransaction can use this to register a delegate to
-// receive notifications when these events happen.
+// Delegate class receiving notifications when cache or network actions start
+// and finish, i.e. when the object starts and finishes waiting on an
+// underlying cache or the network.  The owner of a HttpTransaction can use
+// this to register a delegate to receive notifications when these events
+// happen.
 class HttpTransactionDelegate {
  public:
   virtual ~HttpTransactionDelegate() {}
   virtual void OnCacheActionStart() = 0;
   virtual void OnCacheActionFinish() = 0;
+  virtual void OnNetworkActionStart() = 0;
+  virtual void OnNetworkActionFinish() = 0;
 };
 
 }  // namespace net