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Changing some strings to better portray errors to users and advise
them of what steps they can take next. Both of these are DLC related.
One relates to an error that can occur when a user tries to install
borealis, cancels and tries to install again (before the last
installation has finalized its cancellation). The other relates to the
DLC "Catch-all" error message, where sometimes if users just retry,
the installation will succeed.

Bug: b/171672034, b/172284265
Change-Id: I17ef2028cab27361ec42e0ab581e828d83c72f09
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2544322Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Nic Hollingum <hollingum@google.com>
Commit-Queue: Daniel Ng <danielng@google.com>
Cr-Commit-Position: refs/heads/master@{#828437}