I downloaded the official Chrome nativeMessaging example to test it out.
To do this, I installed the app from chrome://extensions, by choosing Load Unpacked. No problems so far.
I then installed the host. I'm using Windows 7, so I ran install_host.bat, which claimed that "The operation completed successfully." However, when I go to chrome://apps/ and click the Connect button, I get this error:
Failed to connect: Native host has exited.
Is there some reason this would happen? Restarting Chrome did not fix the issue, nor did uninstalling and then reinstalling the host program.
(I noticed that native-messaging-example-host.bat requires Python 2, so I modified it to run Python 2 explicitly. If I run native-messaging-example-host.bat from the command line, it pops up a little example program of its own with a GUI and seems to work correctly.)