[Android WebAPK] Fix LaunchHostBrowserSelector to call callback just once

This CL fixes a bug where the LaunchHostBrowserSelector would be called
twice when a user selects a host browser:
- once with the host browser package
- once with null.
This CL surpresses the second callback by disabling the OnDismissListener
when a 'button is clicked' or 'host browser is chosen'

This CL also fixes the same bug in InstallHostBrowserDialog

BUG=972922

Change-Id: I6b33cc6a600f170e92e44de329f0d3eb24b6f23b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1652291
Reviewed-by: Yaron Friedman <yfriedman@chromium.org>
Commit-Queue: Peter Kotwicz <pkotwicz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#668401}