Propagate error messages to UI for Blimp.
This CL added a Java side UI class to show error messages in Toast or
Snackbar.
Also modified the BlimpClientContext interface for proper error
handling.
Future work: Pulling strings from grd files, this involves some amount
of work, so setup string resources will be done in other CLs.
BUG=
650832
Committed:
https://crrev.com/de3b7c37ab34ad7e6d46f8d205e4e2a449c8fe9b
Cr-Commit-Position: refs/heads/master@{#424453}