Possible fixing for the crash in ChromeAppListModelUpdater

Learnt from other engineers that map::count at some time gives
unexpected results. So replace map::count with map::find in
ChromeAppListModelUpdater::FindItem.

In addition, it is suspected that ActivateChromeItem may affect
|current_model_updater_| in a surprising way. So move ActivateChromeItem
to the end of function. Meanwhile, add more checks to help the bug
investigation.

Bug: 969810
Change-Id: Ic5c7b21efb4746d9761742482d9a697ebe322c44
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1714214Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Andrew Xu <andrewxu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#680088}

chrome/browser/ui/app_list/app_list_client_impl.cc

@@ -191,10 +191,7 @@ void AppListClientImpl::ActivateItem(int profile_id,
     return;
   }
 
-  requested_model_updater->ActivateChromeItem(id, event_flags);
-
   // Send a training signal to the search controller.
-  CHECK(current_model_updater_);
   const auto* item = current_model_updater_->FindItem(id);
   if (item) {
     app_list::AppLaunchData app_launch_data;
@@ -205,6 +202,19 @@ void AppListClientImpl::ActivateItem(int profile_id,
   }
 
   app_launch_event_logger_.OnGridClicked(id);
+
+  requested_model_updater->ActivateChromeItem(id, event_flags);
+
+  // Suspect that |id| may be destructed after calling ActivateChromeItem. Add
+  // the following two lines to help investigate the crash.
+  std::string copy = id;
+  base::debug::Alias(&copy);
+
+  // Suspect that the model updater may change after calling ActivateChromeItem.
+  // Add checks to help invesigate the crash.
+  CHECK(current_model_updater_);
+  CHECK(requested_model_updater);
+  CHECK(current_model_updater_ == requested_model_updater);
 }
 
 void AppListClientImpl::GetContextMenuModel(

chrome/browser/ui/app_list/chrome_app_list_model_updater.cc

@@ -310,7 +310,7 @@ void ChromeAppListModelUpdater::NotifySearchResultItemInstalled(
 // Methods for item querying
 
 ChromeAppListItem* ChromeAppListModelUpdater::FindItem(const std::string& id) {
-  return items_.count(id) ? items_[id].get() : nullptr;
+  return items_.find(id) != items_.end() ? items_[id].get() : nullptr;
 }
 
 size_t ChromeAppListModelUpdater::ItemCount() {