Adding histograms showing fraction of page load times

net/http/http_transaction_delegate.h

Index: net/http/http_transaction_delegate.h
===================================================================
--- net/http/http_transaction_delegate.h	(revision 0)
+++ net/http/http_transaction_delegate.h	(revision 0)
@@ -0,0 +1,24 @@
+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef NET_HTTP_HTTP_TRANSACTION_DELEGATE_H_
+#define NET_HTTP_HTTP_TRANSACTION_DELEGATE_H_
+
+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 transactions on an underlying cache start and
+// finish.
+class HttpTransactionDelegate {
+ public:
+  virtual ~HttpTransactionDelegate() {}
+  virtual void OnCacheActionStart() = 0;
+  virtual void OnCacheActionFinish() = 0;
+};
+
+}  // namespace net
+
+#endif  // NET_HTTP_HTTP_TRANSACTION_DELEGATE_H__