PaymentApp: Implement PaymentAppProvider for LayoutTest.

content/shell/DEPS

 include_rules = [
   "+gin/public",
   "+gin/v8_initializer.h",
   "+v8/include",
 
   # For chromeos build config
   "+chromeos/dbus",
   "+device/bluetooth",  # BluetoothAdapterFactory::Shutdown.
 
   # The content_shell is the canonical sample embedder, so it only uses
   # content's public API.
   "+content/app/strings/grit",  # For generated headers
   "+content/public",
 
   # The content_shell is an embedder so it must work with resource bundles.
   "+ui/base/l10n",
   "+ui/base/resource",
 
   # Shell resources
   "+grit/shell_resources.h",
 
   # The content_shell for aura must work with the views and aura
   "+ui/aura",
   "+ui/views",
 
   # Content Shell can depend on more components than content/, since:
   #   1) it's an example browser
   #   2) it's not linked into the content library
   "+components/crash",
+  "+components/payments/payment_app.mojom.h",
   "+components/url_formatter",
 ]
 
 specific_include_rules = {
   "shell_views\.cc": [
     "+ui/wm/test"
   ],
 }