Our current custom looper implementation tries to handle all messages
including those sent to the main looper. However, the main looper does not
use our doLoop implementation and thus messages never get executed.
This adds a check whether the target looper is the main looper and if so,
uses the default message forwarding implementation.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=194779214
c1e3cb767e