Chrome OS GetHelp: Don't crash on the lock screen.

Make the best effort to determine sizes.

Bug: 1022764
Change-Id: I4b55302b36a2964cd3b11ff8c5c4540c69300bfa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1905550
Commit-Queue: Roman Sorokin [CET] <rsorokin@chromium.org>
Reviewed-by: Roman Aleksandrov <raleksandrov@google.com>
Cr-Commit-Position: refs/heads/master@{#713838}

chrome/browser/chromeos/login/ui/login_web_dialog.cc

@@ -56,8 +56,7 @@ LoginWebDialog::LoginWebDialog(content::BrowserContext* browser_context,
       delegate_(delegate),
       title_(title),
       url_(url) {
-  if (!parent_window_) {
-    DCHECK(chromeos::LoginDisplayHost::default_host());
+  if (!parent_window_ && chromeos::LoginDisplayHost::default_host()) {
     parent_window_ =
         chromeos::LoginDisplayHost::default_host()->GetNativeWindow();
   }
@@ -93,6 +92,11 @@ void LoginWebDialog::GetWebUIMessageHandlers(
     std::vector<WebUIMessageHandler*>* handlers) const {}
 
 void LoginWebDialog::GetDialogSize(gfx::Size* size) const {
+  // TODO(https://crbug.com/1022774): Fix for the lock screen.
+  if (!parent_window_) {
+    *size = kMaxSize;
+    return;
+  }
   gfx::Rect bounds = parent_window_->bounds();
   bounds.Inset(kMinMargins);
   *size = bounds.size();

chrome/browser/chromeos/login/ui/login_web_dialog_browsertest.cc

@@ -45,4 +45,13 @@ IN_PROC_BROWSER_TEST_F(LoginWebDialogTest, CloseDialogByAccelerator) {
   EXPECT_TRUE(closing_observer.widget_closed());
 }
 
+// Tests that LoginWebDialog does not crash with missing parent window.
+IN_PROC_BROWSER_TEST_F(LoginWebDialogTest, NoParentWindow) {
+  LoginWebDialog* dialog = new LoginWebDialog(
+      browser()->profile(), nullptr, nullptr, base::string16(), GURL());
+  dialog->Show();
+  aura::Window* window = dialog->get_dialog_window_for_test();
+  ASSERT_TRUE(window);
+}
+
 }  // namespace chromeos