This just means that you are using chromium builds. These are built without API keys baked in. The solution is either to
a) build/use Chrome branded binaries or
b) instruct user to install personal API keys in /etc/chrome_dev.conf

For (a), 
https://sites.google.com/a/google.com/chrome-te/home/tools/bisect-builds
indicates that I should use the -o flag, but that appears to have been removed by https://codereview.chromium.org/1970613004.  Is there a new, preferred way to bisect on official builds?

Does (b) work when I'm running on my Linux desktop?  If so, where would I put the chrome_dev.conf so that downloaded bisect builds would find it?

b) You put the keys in environmnent variables, see bottom of
https://www.chromium.org/developers/how-tos/api-keys

a) I don't have experience with -o.

> b) You put the keys in environmnent variables, see bottom of
> https://www.chromium.org/developers/how-tos/api-keys

Right, the "Providing Keys at Runtime" section says to put the keys in /etc/chrome_dev.conf, which I assume would work if I was running on a device.  But I'm running the bisect on my Linux desktop, and putting chrome_dev.conf in my file system's /etc directory isn't working.  So I'm wondering, once I've got the API keys in chrome_dev.conf, where do I put that file in my Linux desktop filesystem so that the bisect binaries (which are being downloaded to and run from a temp directory like "/tmp/bisect_tmphAP7v3/chrome-linux") can find and use them?

You can set the environment variables directly, I just tried it and it works.

Googlers can search for "simplified_approach_for_chrome_api_keys" in our internal docs

Indeed, on a desktop you just put the keys in the environment variables without a need for chrome_dev.conf.

Ah, got it... that's the bit I was missing.  Thanks for the info!  I've added a comment to https://sites.google.com/a/chromium.org/dev/developers/bisect-builds-py .  Once that gets updated, I'll consider the matter resolved to my satisfaction :-)

You can edit the page with your chromium account. Just sign in on the bottom and then edit (I think on top).

Updated https://sites.google.com/a/chromium.org/dev/developers/bisect-builds-py , so the fix is now hopefully easy to find.