Fix the Crash in the launcher's start page on Chrome OS.

ui/app_list/views/start_page_view.cc

 // Copyright 2014 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.
 
 #include "ui/app_list/views/start_page_view.h"
 
 #include <algorithm>
 #include <string>
 
 #include "base/i18n/rtl.h"
@@ skipping 154 matching lines @@
 TileItemView* StartPageView::StartPageTilesContainer::GetTileItemView(
     int index) {
   DCHECK_GT(num_results(), index);
   if (index == num_results() - 1)
     return all_apps_button_;
 
   return search_result_tile_views_[index];
 }
 
 int StartPageView::StartPageTilesContainer::Update() {
+  std::vector<SearchResult*> display_results =
+      AppListModel::FilterSearchResultsByDisplayType(
+          results(), SearchResult::DISPLAY_RECOMMENDATION, kNumStartPageTiles);
+
   // Ignore updates and disable buttons when transitioning to a different
   // state.
   if (contents_view_->GetActiveState() != AppListModel::STATE_START) {
     for (auto* view : search_result_tile_views_)
       view->SetEnabled(false);
 
-    return num_results();
+    // We still need to update the number: add 1 to the results size to account
+    // for the all apps button.
+    return display_results.size() + 1;

[xiyuan, 2017/01/03 17:05:13]

Not sure whether this is the right thing to do. We will update num_results()
when this returns. However, |search_result_tile_views_| is not changed and
GetTileItemView probably will not work properly because of that, e.g.
display_results.size() + 1 is greater than old num_results and GetTileItemView
tries to access beyond the old num_results.

[xdai1, 2017/01/03 19:15:41]

Emmm... In this case the approach in the first patch might be better?
StartPageTilesContainer::Update() is not only called by
SearchResultContainerView::DoUpdate() but also can be called by
StartPageView::OnShown() (the state is AppListModel::STATE_START), which I think
is the case here. From the bug's crash stack, the crash is caused by the
keyboard navigation gesture StartPageView::OnKeyPressed() which is guaranteed to
be called after StartPageView::OnShown(). Thus if we call ScheduleUpdate() in
StartPageTilesContainer::Update(), num_results() and |search_result_tile_views_|
are forced to be updated to prevent the crash. Or maybe we can expose a
set_num_results() function and call it in StartPageView::OnShown()? Suggestions?

   }
 
-  std::vector<SearchResult*> display_results =
-      AppListModel::FilterSearchResultsByDisplayType(
-          results(), SearchResult::DISPLAY_RECOMMENDATION, kNumStartPageTiles);
   if (display_results.size() != search_result_tile_views_.size()) {
     // We should recreate the grid layout in this case.
     for (size_t i = 0; i < search_result_tile_views_.size(); ++i)
       delete search_result_tile_views_[i];
     search_result_tile_views_.clear();
     RemoveChildView(all_apps_button_);
-    CreateAppsGrid(std::min(kNumStartPageTiles, display_results.size()));

[xiyuan, 2017/01/03 17:05:14]

Would this change have side effect that we might display too many items on start
page?

[xdai1, 2017/01/03 19:15:41]

The maximum number of |display_results| is kNumStartPageTiles, so we should be
fine here. See line 184-186 in this patch.

+    CreateAppsGrid(display_results.size());
   }
 
   // Update the tile item results.
   for (size_t i = 0; i < search_result_tile_views_.size(); ++i) {
     SearchResult* item = nullptr;
     if (i < display_results.size())
       item = display_results[i];
     search_result_tile_views_[i]->SetSearchResult(item);
     search_result_tile_views_[i]->SetEnabled(true);
   }
 
   Layout();
   parent()->Layout();
   // Add 1 to the results size to account for the all apps button.
   return display_results.size() + 1;
 }
 
 void StartPageView::StartPageTilesContainer::UpdateSelectedIndex(
     int old_selected,
     int new_selected) {
-  if (old_selected >= 0)
+  if (old_selected >= 0 && old_selected < num_results())
     GetTileItemView(old_selected)->SetSelected(false);
 
-  if (new_selected >= 0)
+  if (new_selected >= 0 && new_selected < num_results())
     GetTileItemView(new_selected)->SetSelected(true);
 }
 
 void StartPageView::StartPageTilesContainer::OnContainerSelected(
     bool /*from_bottom*/,
     bool /*directional_movement*/) {
   NOTREACHED();
 }
 
 void StartPageView::StartPageTilesContainer::NotifyFirstResultYIndex(
@@ skipping 299 matching lines @@
   // is enabled).
   if (event->type() == ui::ET_SCROLL && event->y_offset() < 0)
     MaybeOpenCustomLauncherPage();
 }
 
 TileItemView* StartPageView::GetTileItemView(size_t index) {
   return tiles_container_->GetTileItemView(index);
 }
 
 }  // namespace app_list