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The fake device used to just CHECK when it failed to read the file,
but I noticed those checks don't make it into the logs for official
builds. This makes the --use-file-for-fake-audio-capture flag a bit
user-hostile, which has also shown up in Chrome crash reports. This
way there will be an entry in the log and the device will be silent
instead of crashing.

BUG=466408

Review URL: https://codereview.chromium.org/1018293002

Cr-Commit-Position: refs/heads/master@{#321365}