Notification scheduler: Remove sort for impression tracker.

This CL removes the sorting for impressions. Also move the logic that
prunes expired impressions to the point when the database is just
initialized.

This can save APK size by 4000 bytes according to diagnose_bloat.py.

Resource Sizes Diff:
Specifics:
        -4,096 bytes main lib size
        -4,002 bytes normalized apk size
InstallSize:
        -4,098 bytes APK size
        -4,098 bytes Estimated installed size (Android Go)
        -4,098 bytes Estimated installed size
InstallBreakdown (-4,098 bytes):
        -4,096 bytes Native code size
            -2 bytes Package metadata size

Bug: 972191
Change-Id: Ic6f2e971fb12de5c3b5affabd11c26b4512ea170
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1761331Reviewed-by: David Trainor <dtrainor@chromium.org>
Commit-Queue: Xing Liu <xingliu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#688336}

chrome/browser/notifications/scheduler/internal/impression_history_tracker.cc

@@ -15,11 +15,6 @@
 namespace notifications {
 namespace {
 
-// Comparator used to sort notification entries based on creation time.
-bool CreateTimeCompare(const Impression& lhs, const Impression& rhs) {
-  return lhs.create_time < rhs.create_time;
-}
-
 std::string ToDatabaseKey(SchedulerClientType type) {
   switch (type) {
     case SchedulerClientType::kTest1:
@@ -151,16 +146,25 @@ void ImpressionHistoryTrackerImpl::OnStoreInitialized(
 
   initialized_ = true;
 
-  // Load the data to memory, and sort the impression list.
+  // Load the data to memory, and prune expired impressions.
+  auto now = clock_->Now();
   for (auto it = entries.begin(); it != entries.end(); ++it) {
     auto& entry = (*it);
     auto type = entry->type;
-    std::sort(entry->impressions.begin(), entry->impressions.end(),
-              &CreateTimeCompare);
+    ClientState::Impressions impressions;
     for (auto& impression : entry->impressions) {
-      impression_map_.emplace(impression.guid, &impression);
+      bool expired =
+          now - impression.create_time > config_.impression_expiration;
+      if (expired) {
+        SetNeedsUpdate(type, true);
+      } else {
+        impressions.emplace_back(impression);
+        impression_map_.emplace(impression.guid, &impressions.back());
+      }
     }
+    entry->impressions.swap(impressions);
     client_states_.emplace(type, std::move(*it));
+    MaybeUpdateDb(type);
   }
 
   SyncRegisteredClients();
@@ -200,17 +204,6 @@ void ImpressionHistoryTrackerImpl::AnalyzeImpressionHistory(
     ClientState* client_state) {
   DCHECK(client_state);
   base::circular_deque<Impression*> dismisses;
-  base::Time now = clock_->Now();
-
-  // Prune out expired impression.
-  while (!client_state->impressions.empty() &&
-         now - client_state->impressions.front().create_time >
-             config_.impression_expiration) {
-    impression_map_.erase(client_state->impressions.front().guid);
-    client_state->impressions.pop_front();
-    SetNeedsUpdate(client_state->type, true);
-  }
-
   for (auto it = client_state->impressions.begin();
        it != client_state->impressions.end(); ++it) {
     auto* impression = &*it;

chrome/browser/notifications/scheduler/internal/impression_history_tracker_unittest.cc

@@ -210,20 +210,13 @@ TEST_F(ImpressionHistoryTrackerTest, DeleteExpiredImpression) {
   Impression expired = CreateImpression(expired_create_time, "guid1");
   Impression not_expired = CreateImpression(not_expired_time, "guid2");
 
-  // The impressions in the input should be sorted by creation time when gets
-  // loaded to memory.
   test_case.input.back().impressions = {expired, not_expired, expired};
-
-  // Expired impression created in |expired_create_time| should be deleted.
-  // No change expected on the next impression, which is not expired and no user
-  // feedback .
   test_case.expected.back().impressions = {not_expired};
 
   CreateTracker(test_case);
-  InitTrackerWithData(test_case);
   EXPECT_CALL(*store(), Update(_, _, _));
-  EXPECT_CALL(*delegate(), OnImpressionUpdated());
-  tracker()->AnalyzeImpressionHistory();
+  InitTrackerWithData(test_case);
+  EXPECT_CALL(*delegate(), OnImpressionUpdated()).Times(0);
   VerifyClientStates(test_case);
 }