[CrOS MultiDevice] Add missing scripts to chrome://proximity-auth.

These scripts were erroneously omitted from the page, resulting in a
DCHECK() failure.

Change-Id: I9b1ccb554d096767d949ede14914aae13d00fbdc
Reviewed-on: https://chromium-review.googlesource.com/c/1354133Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Reviewed-by: Ryan Hansberry <hansberry@chromium.org>
Commit-Queue: Kyle Horimoto <khorimoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#611932}

chromeos/components/proximity_auth/webui/resources/proximity_auth.html

@@ -12,6 +12,8 @@
   <script src="logs.js"></script>
   <script src="proximity_auth.js"></script>
   <script src="chrome://resources/js/mojo_bindings.js"></script>
+  <script src="chrome://resources/js/time.mojom.js"></script>
+  <script src="chrome://resources/js/chromeos/device_sync.mojom.js"></script>
   <script src="chrome://resources/js/chromeos/multidevice_setup.mojom.js">
   </script>
   <script src="chrome://resources/js/chromeos/multidevice_setup_constants.mojom.js">