Fix payment dialog background color with GTK theme

BUG=914974
R=pkasting

Change-Id: Ia017ddb1cb1314bea83c29b5dd9a313cf60e717b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2076098
Auto-Submit: Thomas Anderson <thomasanderson@chromium.org>
Reviewed-by: Peter Kasting <pkasting@chromium.org>
Commit-Queue: Peter Kasting <pkasting@chromium.org>
Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#744818}

chrome/browser/ui/views/autofill/payments/card_unmask_prompt_views.cc

@@ -242,6 +242,7 @@ void CardUnmaskPromptViews::AddedToWidget() {
 }
 
 void CardUnmaskPromptViews::OnThemeChanged() {
+  views::BubbleDialogDelegateView::OnThemeChanged();
   SkColor bg_color = GetNativeTheme()->GetSystemColor(
       ui::NativeTheme::kColorId_DialogBackground);
   overlay_->SetBackground(views::CreateSolidBackground(bg_color));