Adding DRP specfic UMA for FirstContentfulPaint

content/browser/frame_host/navigation_user_data.h

+// Copyright 2014 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 CONTENT_BROWSER_FRAME_HOST_NAVIGATION_USER_DATA_H_
+#define CONTENT_BROWSER_FRAME_HOST_NAVIGATION_USER_DATA_H_
+
+#include "base/macros.h"
+#include "base/supports_user_data.h"
+
+namespace content {
+
+extern const void* const kNavigationUserDataKey;
+
+class NavigationSupportsUserData : public base::SupportsUserData {
+ public:
+  NavigationSupportsUserData() {}
+  ~NavigationSupportsUserData() override {}
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(NavigationSupportsUserData);
+};
+
+class NavigationUserData : public base::SupportsUserData::Data {
+ public:
+  NavigationUserData();
+  NavigationSupportsUserData* get_navigation_supports_user_data();

[RyanSturm, 2016/03/24 17:43:06]

Consider changing to SetUserData(void* key, Data data). With this interface
change, we can ensure no dangling references are left on the IO thread. It is
important that the only way a reference to NavigationSupportsUserData gets out
is if ownership transfers with it. Essentially, this change forces the
NavigationUserData to be write only.

+  scoped_ptr<NavigationSupportsUserData>
+  take_own_navigation_supports_user_data();
+
+  ~NavigationUserData() override;
+
+ private:
+  scoped_ptr<NavigationSupportsUserData> navigation_supports_user_data_;
+  DISALLOW_COPY_AND_ASSIGN(NavigationUserData);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_FRAME_HOST_NAVIGATION_USER_DATA_H_