app_list: check AppListClient pointer in AppListControllerImpl.

This commit skips some logic when the AppListClient pointer is not set
in AppListControllerImpl. This makes clusterfuzz happy at this point,
and avoids potential crashes in the future.

Bug: 824104
Bug: 733662
Change-Id: I82612d59ae23e843e47192a4254080f4a8fa67fd
Reviewed-on: https://chromium-review.googlesource.com/1015220
Commit-Queue: Jiaquan He <hejq@google.com>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#551419}

ash/app_list/app_list_controller_impl.cc

@@ -330,12 +330,13 @@ void AppListControllerImpl::OnSessionStateChanged(
 
 void AppListControllerImpl::OnAppListItemWillBeDeleted(
     app_list::AppListItem* item) {
-  if (item->is_folder())
+  if (client_ && item->is_folder())
     client_->OnFolderDeleted(item->CloneMetadata());
 }
 
 void AppListControllerImpl::OnAppListItemUpdated(app_list::AppListItem* item) {
-  client_->OnItemUpdated(item->CloneMetadata());
+  if (client_)
+    client_->OnItemUpdated(item->CloneMetadata());
 }
 
 ////////////////////////////////////////////////////////////////////////////////
@@ -470,60 +471,72 @@ bool AppListControllerImpl::IsHomeLauncherEnabledInTabletMode() const {
 // Methods of |client_|:
 
 void AppListControllerImpl::StartSearch(const base::string16& raw_query) {
-  client_->StartSearch(raw_query);
+  if (client_)
+    client_->StartSearch(raw_query);
 }
 
 void AppListControllerImpl::OpenSearchResult(const std::string& result_id,
                                              int event_flags) {
-  client_->OpenSearchResult(result_id, event_flags);
+  if (client_)
+    client_->OpenSearchResult(result_id, event_flags);
 }
 
 void AppListControllerImpl::InvokeSearchResultAction(
     const std::string& result_id,
     int action_index,
     int event_flags) {
-  client_->InvokeSearchResultAction(result_id, action_index, event_flags);
+  if (client_)
+    client_->InvokeSearchResultAction(result_id, action_index, event_flags);
 }
 
 void AppListControllerImpl::ViewShown(int64_t display_id) {
-  client_->ViewShown(display_id);
+  if (client_)
+    client_->ViewShown(display_id);
 }
 
 void AppListControllerImpl::ViewClosing() {
-  client_->ViewClosing();
+  if (client_)
+    client_->ViewClosing();
 }
 
 void AppListControllerImpl::ActivateItem(const std::string& id,
                                          int event_flags) {
-  client_->ActivateItem(id, event_flags);
+  if (client_)
+    client_->ActivateItem(id, event_flags);
 }
 
 void AppListControllerImpl::GetContextMenuModel(
     const std::string& id,
     GetContextMenuModelCallback callback) {
-  client_->GetContextMenuModel(id, std::move(callback));
+  if (client_)
+    client_->GetContextMenuModel(id, std::move(callback));
 }
 
 void AppListControllerImpl::ContextMenuItemSelected(const std::string& id,
                                                     int command_id,
                                                     int event_flags) {
-  client_->ContextMenuItemSelected(id, command_id, event_flags);
+  if (client_)
+    client_->ContextMenuItemSelected(id, command_id, event_flags);
 }
 
 void AppListControllerImpl::OnVisibilityChanged(bool visible) {
-  client_->OnAppListVisibilityChanged(visible);
+  if (client_)
+    client_->OnAppListVisibilityChanged(visible);
 }
 
 void AppListControllerImpl::OnTargetVisibilityChanged(bool visible) {
-  client_->OnAppListTargetVisibilityChanged(visible);
+  if (client_)
+    client_->OnAppListTargetVisibilityChanged(visible);
 }
 
 void AppListControllerImpl::StartVoiceInteractionSession() {
-  client_->StartVoiceInteractionSession();
+  if (client_)
+    client_->StartVoiceInteractionSession();
 }
 
 void AppListControllerImpl::ToggleVoiceInteractionSession() {
-  client_->ToggleVoiceInteractionSession();
+  if (client_)
+    client_->ToggleVoiceInteractionSession();
 }
 
 ////////////////////////////////////////////////////////////////////////////////