Modern Chromebooks support Android out-of-the-box. Older models may support it, but not "officially", and need a workaround to get Android going.
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Enable Developer Mode. See: https://developer.android.com/topic/arc/sideload.html#enter-dev
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Enter the shell and create a file called
/usr/local/etc/chrome_dev.conf
with these contents:
--enable-arc
--arc-availability=officially-supported