Include tab IDs when reporting data use accounting.

chrome/browser/data_usage/tab_id_provider.h

+// Copyright (c) 2015 The Chromium Authors. All rights reserved.

[bengr, 2015/11/05 00:00:38]

"(c)" -> ""

[sclittle, 2015/11/05 01:22:48]

Done.

+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROME_BROWSER_DATA_USAGE_TAB_ID_PROVIDER_H_
+#define CHROME_BROWSER_DATA_USAGE_TAB_ID_PROVIDER_H_
+
+#include <stdint.h>
+
+#include "base/callback_forward.h"
+#include "base/macros.h"
+#include "base/memory/weak_ptr.h"
+#include "base/supports_user_data.h"
+#include "base/threading/thread_checker.h"
+
+namespace base {
+class TaskRunner;
+}
+
+namespace tracked_objects {
+class Location;
+}
+
+namespace chrome_browser_data_usage {
+
+// Object that can be attached to a URLRequest to provide the tab ID of that
+// URLRequest to callbacks that want them. Callbacks are either run immediately
+// if the tab ID is already available, or queued to be run later once the tab ID
+// becomes available.
+class TabIdProvider : public base::SupportsUserData::Data {
+ public:
+  // Constructs a tab ID provider, posting the |tab_id_getter| task onto
+  // |task_runner|.
+  TabIdProvider(base::TaskRunner* task_runner,
+                const tracked_objects::Location& from_here,
+                const base::Callback<int32_t(void)>& tab_id_getter);
+
+  ~TabIdProvider() override;
+
+  // Calls |callback| with the tab ID, either immediately if it's already
+  // available, or later once it becomes available.
+  void ProvideTabId(const base::Callback<void(int32_t)>& callback);
+
+  base::WeakPtr<TabIdProvider> GetWeakPtr();
+
+  static const void* kUserDataKey;
+
+ private:
+  class CallbackRunner;
+
+  // Called when the |tab_id| is ready.
+  void OnTabIdReady(int32_t tab_id);
+
+  base::ThreadChecker thread_checker_;
+  bool is_tab_id_ready_;

[bengr, 2015/11/05 00:00:38]

Why do you need both a tab_id and this? Couldn't initializing tab_id to -1
suffice? Please add a comment to explain.

[sclittle, 2015/11/05 01:22:48]

-1 is special, it means that no tab ID was found, it doesn't mean that we're
still waiting for a tab ID. It's possible that the tab ID getter could return -1
("no tab ID was found"), and we should cache that -1 here and provide that to
whoever wants it.

+  int32_t tab_id_;
+  base::WeakPtr<CallbackRunner> weak_callback_runner_;
+  base::WeakPtrFactory<TabIdProvider> weak_ptr_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(TabIdProvider);
+};
+
+}  // namespace chrome_browser_data_usage
+
+#endif  // CHROME_BROWSER_DATA_USAGE_TAB_ID_PROVIDER_H_