So, that was weird. Suddenly, out of nowhere, the opengl sample I was working on for native client stopped working. So I backed out of my code. Still didn't work. Checked my other samples. They didn't work either. Looked at Assaf's Ogre3D sample. Even it didn't work. Started checking my flags and browser settings. Everything looked hunky dory.
Turns out that when you're subscribed to the Chrome developer channel, your version of Chrome will auto-update to whatever the latest offering in the channel is. And it turns out that to keep up with changes in the API, Chrome changed. Normally useful and good for security, but a problem when I'm developing - if Chrome silently updates itself behind the scenes, with breaking changes, I'm going to assume it was something I did.
So - is there a way to turn it off? No.
BUT - I can use Chromium, the open-source sibling of Chrome - its build history is kept on line here. The version I wanted was here - the file I was looking for was chrome-win32.zip. After unzipping that into a Chromium directory in my root I was able to work again. So I'm going to stick with Chromium builds from here out, until I'm done working with Google classes that have the "_dev" suffix.