Web MIDI: Upgrade sysex authority on demand

Currently, MidiHost caches sysex authority on the session start, that
means when the first client connects. But the second or later clients
share the same session, and may have different authority.

This patch changes to update the cached authority when permission
checks fail.

Bug: 912501
Change-Id: I6fc4ebe456c7a62c4f9bc96f8332a1e78d522cb0
Reviewed-on: https://chromium-review.googlesource.com/c/1390891
Commit-Queue: Takashi Toyoshima <toyoshim@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Reviewed-by: Adithya Srinivasan <adithyas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#625168}
3 files changed