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

chrome/browser/android/data_usage has a few uses of std::deque that
would work just about as well using std::vector, and since std::deque is
memory inefficient for small numbers of elements (see
http://crbug.com/674287), this CL replaces those uses of std::deque with
std::vector.

BUG=679568

Review-Url: https://codereview.chromium.org/2624663002
Cr-Commit-Position: refs/heads/master@{#443066}

chrome/browser/android/data_usage/external_data_use_observer.cc

@@ -134,7 +134,7 @@ void ExternalDataUseObserver::OnDataUse(const data_usage::DataUse& data_use) {
   DCHECK(registered_as_data_use_observer_);
 
   if (!data_use_list_) {
-    data_use_list_.reset(new std::deque<const data_usage::DataUse>());
+    data_use_list_.reset(new std::vector<const data_usage::DataUse>());
     // Post a task to the same IO thread, that will get invoked when some of the
     // data use objects are batched.
     io_task_runner_->PostTask(

chrome/browser/android/data_usage/external_data_use_observer.h

@@ -5,8 +5,8 @@
 #ifndef CHROME_BROWSER_ANDROID_DATA_USAGE_EXTERNAL_DATA_USE_OBSERVER_H_
 #define CHROME_BROWSER_ANDROID_DATA_USAGE_EXTERNAL_DATA_USE_OBSERVER_H_
 
-#include <deque>
 #include <memory>
+#include <vector>
 
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
@@ -116,7 +116,7 @@ class ExternalDataUseObserver : public data_usage::DataUseAggregator::Observer {
   // Batches the data use objects reported by DataUseAggregator. This will be
   // created when data use batching starts and released when the batching ends.
   // This will be null if there is no ongoing batching of data use objects.
-  std::unique_ptr<std::deque<const data_usage::DataUse>> data_use_list_;
+  std::unique_ptr<std::vector<const data_usage::DataUse>> data_use_list_;
 
   // |io_task_runner_| is used to call methods on IO thread.
   scoped_refptr<base::SingleThreadTaskRunner> io_task_runner_;

chrome/browser/android/data_usage/external_data_use_reporter.cc

@@ -131,7 +131,7 @@ ExternalDataUseReporter::~ExternalDataUseReporter() {
 }
 
 void ExternalDataUseReporter::OnDataUse(
-    std::unique_ptr<const std::deque<const data_usage::DataUse>>
+    std::unique_ptr<const std::vector<const data_usage::DataUse>>
         data_use_list) {
   DCHECK(thread_checker_.CalledOnValidThread());
   DCHECK(data_use_list);

chrome/browser/android/data_usage/external_data_use_reporter.h

@@ -8,9 +8,9 @@
 #include <stddef.h>
 #include <stdint.h>
 
-#include <deque>
 #include <memory>
 #include <string>
+#include <vector>
 
 #include "base/callback.h"
 #include "base/containers/hash_tables.h"
@@ -86,7 +86,7 @@ class ExternalDataUseReporter {
   // Notifies the ExternalDataUseReporter of data usage. The data use is labeled
   // using |data_use_tab_model_|, buffered and then reported to
   // |external_data_use_observer_bridge_| later.
-  void OnDataUse(std::unique_ptr<const std::deque<const data_usage::DataUse>>
+  void OnDataUse(std::unique_ptr<const std::vector<const data_usage::DataUse>>
                      data_use_list);
 
   void OnReportDataUseDone(bool success);

chrome/browser/android/data_usage/external_data_use_reporter_unittest.cc

@@ -127,8 +127,8 @@ class ExternalDataUseReporterTest : public testing::Test {
   }
 
   void OnDataUse(const data_usage::DataUse& data_use) {
-    std::unique_ptr<std::deque<const data_usage::DataUse>> data_use_list(
-        new std::deque<const data_usage::DataUse>());
+    std::unique_ptr<std::vector<const data_usage::DataUse>> data_use_list(
+        new std::vector<const data_usage::DataUse>());
     data_use_list->push_back(data_use);
     external_data_use_reporter()->OnDataUse(std::move(data_use_list));
   }

chrome/browser/android/data_usage/tab_data_use_entry.cc

@@ -129,7 +129,7 @@ bool TabDataUseEntry::IsTrackingDataUse() const {
   return back_iterator->end_time.is_null();
 }
 
-const base::TimeTicks TabDataUseEntry::GetLatestStartOrEndTime() const {
+base::TimeTicks TabDataUseEntry::GetLatestStartOrEndTime() const {
   TabSessions::const_reverse_iterator back_iterator = sessions_.rbegin();
   if (back_iterator == sessions_.rend())
     return base::TimeTicks();  // No tab session found.
@@ -140,7 +140,7 @@ const base::TimeTicks TabDataUseEntry::GetLatestStartOrEndTime() const {
   return back_iterator->start_time;
 }
 
-const std::string TabDataUseEntry::GetActiveTrackingSessionLabel() const {
+std::string TabDataUseEntry::GetActiveTrackingSessionLabel() const {
   TabSessions::const_reverse_iterator back_iterator = sessions_.rbegin();
   if (back_iterator == sessions_.rend() || !IsTrackingDataUse())
     return std::string();
@@ -155,16 +155,22 @@ void TabDataUseEntry::set_custom_tab_package_match(
 }
 
 void TabDataUseEntry::CompactSessionHistory() {
-  while (sessions_.size() > tab_model_->max_sessions_per_tab()) {
-    const auto& front = sessions_.front();
-    DCHECK(!front.end_time.is_null());
+  if (sessions_.size() <= tab_model_->max_sessions_per_tab())
+    return;
+
+  const auto end_it = sessions_.begin() +
+                      (sessions_.size() - tab_model_->max_sessions_per_tab());
+
+  for (auto it = sessions_.begin(); it != end_it; ++it) {
+    DCHECK(!it->end_time.is_null());
     // Track how often old sessions are lost.
     UMA_HISTOGRAM_CUSTOM_TIMES(kUMAOldInactiveSessionRemovalDurationHistogram,
-                               tab_model_->NowTicks() - front.end_time,
+                               tab_model_->NowTicks() - it->end_time,
                                base::TimeDelta::FromSeconds(1),
                                base::TimeDelta::FromHours(1), 50);
-    sessions_.pop_front();
   }
+
+  sessions_.erase(sessions_.begin(), end_it);
 }
 
 }  // namespace android

chrome/browser/android/data_usage/tab_data_use_entry.h

@@ -5,8 +5,8 @@
 #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"
@@ -26,10 +26,10 @@ struct TabDataUseTrackingSession {
       : 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.
@@ -81,11 +81,11 @@ class TabDataUseEntry {
 
   // 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_;
@@ -101,7 +101,11 @@ class TabDataUseEntry {
                            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.

chrome/browser/android/data_usage/tab_data_use_entry_unittest.cc

@@ -163,7 +163,7 @@ class TabDataUseEntryTest : public testing::Test {
 };
 
 // Starts a single tracking session and checks if a new active session is added
-// to the deque. Ends the session and checks if it becomes inactive.
+// to the vector. Ends the session and checks if it becomes inactive.
 TEST_F(TabDataUseEntryTest, SingleTabSessionStartEnd) {
   ExpectTabEntrySessionsSize(TabEntrySessionSize::ZERO);
   EXPECT_FALSE(tab_entry_->IsTrackingDataUse());
@@ -178,7 +178,7 @@ TEST_F(TabDataUseEntryTest, SingleTabSessionStartEnd) {
 }
 
 // Starts multiple tracking sessions and checks if new active sessions are added
-// to the deque for each. Ends the sessions and checks if they become inactive.
+// to the vector for each. Ends the sessions and checks if they become inactive.
 TEST_F(TabDataUseEntryTest, MultipleTabSessionStartEnd) {
   ExpectTabEntrySessionsSize(TabEntrySessionSize::ZERO);
   EXPECT_FALSE(tab_entry_->IsTrackingDataUse());