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In ArcOemCryptoBridger and ArcMidisBridge, Mojo connection error
was not handled, so it caused a crash.
This CL handles the errors.

BUG=None
TEST=Ran on DUT.

Change-Id: Ib6fa54109ac4da03cf9d6e6386d038c92e22357b
Reviewed-on: https://chromium-review.googlesource.com/c/1286098Reviewed-by: Yusuke Sato <yusukes@chromium.org>
Commit-Queue: Hidehiko Abe <hidehiko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#601858}