ash: Set in-session auth dialog bounds according to parent window

This change sets the bounds of the in-session auth dialog according
to the parent window bounds and the contents view's preferred size.

This also fixes a bug introduced in http://crrev/c/2441963 where the
dialog was not shown because no bound was specified and the contents
view uses FillLayout.

Bug: b/156258540
Change-Id: I30f863ded3eb1a7b6ec20c88a0bb46c1d23cd4cf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2504638
Commit-Queue: Yicheng Li <yichengli@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#823444}

ash/in_session_auth/in_session_auth_dialog.cc

@@ -16,8 +16,9 @@
 namespace ash {
 namespace {
 
-// The initial height does nothing except determining the vertical position of
-// the dialog, since the dialog is centered with the initial height.
+// The top inset value is set such that the dialog overlaps with the browser
+// address bar, for anti-spoofing.
+constexpr int kTopInsetDp = 36;
 constexpr int kCornerRadius = 12;
 
 std::unique_ptr<views::Widget> CreateAuthDialogWidget(
@@ -51,6 +52,13 @@ InSessionAuthDialog::InSessionAuthDialog(uint32_t auth_methods,
     : auth_methods_(auth_methods) {
   widget_ = CreateAuthDialogWidget(
       std::make_unique<AuthDialogContentsView>(auth_methods), parent_window);
+  gfx::Rect bounds = parent_window->GetBoundsInScreen();
+  gfx::Size preferred_size = widget_->GetContentsView()->GetPreferredSize();
+  int horizontal_inset_dp = (bounds.width() - preferred_size.width()) / 2;
+  int bottom_inset_dp = bounds.height() - kTopInsetDp - preferred_size.height();
+  bounds.Inset(horizontal_inset_dp, kTopInsetDp, horizontal_inset_dp,
+               bottom_inset_dp);
+  widget_->SetBounds(bounds);
 
   aura::Window* window = widget_->GetNativeWindow();
   rounded_corner_decorator_ = std::make_unique<RoundedCornerDecorator>(