Changed uses of deque to vector in chrome/browser/android/data_usage.

chrome/browser/android/data_usage/tab_data_use_entry.h

 // Copyright 2015 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 CHROME_BROWSER_ANDROID_DATA_USAGE_TAB_DATA_USE_ENTRY_H_
 #define CHROME_BROWSER_ANDROID_DATA_USAGE_TAB_DATA_USE_ENTRY_H_
 
-#include <deque>
 #include <string>
+#include <vector>
 
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "base/time/time.h"
 
 namespace chrome {
 
 namespace android {
 
 class DataUseTabModel;
 
 // TabDataUseTrackingSession maintains the information about a single tracking
 // session within a browser tab.
 struct TabDataUseTrackingSession {
   TabDataUseTrackingSession(const std::string& label,
                             const base::TimeTicks& start_time)
       : label(label), start_time(start_time) {}
 
   // Tracking label to be associated with the data usage of this session.
-  const std::string label;
+  std::string label;
 
   // Time the data use tracking session started.
-  const base::TimeTicks start_time;
+  base::TimeTicks start_time;
 
   // Time the data use tracking session ended. |end_time| will be null if the
   // tracking session is currently active.
   base::TimeTicks end_time;
 };
 
 // TabDataUseEntry contains the history of the disjoint tracking sessions for a
 // single browser tab.
 class TabDataUseEntry {
  public:
@@ skipping 31 matching lines @@
   bool IsTrackingDataUse() const;
 
   // Returns true if the tab has expired. A closed tab entry expires
   // |kClosedTabExpirationDurationSeconds| seconds after it was closed. An open
   // tab entry expires |kOpenTabExpirationDurationSeconds| seconds after the
   // most recent tracking session start or end event.
   bool IsExpired() const;
 
   // Returns the latest time a tracking session was started or ended. Returned
   // time will be null if no tracking session was ever started or ended.
-  const base::TimeTicks GetLatestStartOrEndTime() const;
+  base::TimeTicks GetLatestStartOrEndTime() const;
 
   // Returns the tracking label for the active tracking session. Empty string is
   // returned if tracking session is not active.
-  const std::string GetActiveTrackingSessionLabel() const;
+  std::string GetActiveTrackingSessionLabel() const;
 
   bool is_custom_tab_package_match() const {
     return is_custom_tab_package_match_;
   }
 
   void set_custom_tab_package_match(bool is_custom_tab_package_match);
 
  private:
   friend class TabDataUseEntryTest;
   FRIEND_TEST_ALL_PREFIXES(TabDataUseEntryTest, MultipleTabSessionCloseEvent);
   FRIEND_TEST_ALL_PREFIXES(TabDataUseEntryTest, SingleTabSessionCloseEvent);
   FRIEND_TEST_ALL_PREFIXES(DataUseTabModelTest,
                            ExpiredInactiveTabEntryRemovaltimeHistogram);
   FRIEND_TEST_ALL_PREFIXES(DataUseTabModelTest, TabCloseEvent);
 
-  typedef std::deque<TabDataUseTrackingSession> TabSessions;
+  // This is a std::vector instead of a std::deque because std::deque is
+  // inefficient for small numbers of elements (see crbug/674287). By default,
+  // at most 5 sessions are tracked at a time per tab, so erasing from the front
+  // of the vector is cheap anyways.
+  typedef std::vector<TabDataUseTrackingSession> TabSessions;
 
   // Compacts the history of tracking sessions by removing oldest sessions to
   // keep the size of |sessions_| within |kMaxSessionsPerTab| entries.
   void CompactSessionHistory();
 
   // Contains the history of sessions in chronological order. Oldest sessions
   // will be at the front of the queue, and new sessions will get added to the
   // end of the queue.
   TabSessions sessions_;
 
   // Indicates the time the tab was closed. |tab_close_time_| will be null if
   // the tab is still open.
   base::TimeTicks tab_close_time_;
 
   // True if tracking was started in a custom tab due to package name match.
   bool is_custom_tab_package_match_;
 
   // Pointer to the DataUseTabModel that owns |this|.
   const DataUseTabModel* tab_model_;
 };
 
 }  // namespace android
 
 }  // namespace chrome
 
 #endif  // CHROME_BROWSER_ANDROID_DATA_USAGE_TAB_DATA_USE_ENTRY_H_