Bisect:
436652 (good) - 436659 (bad), 57.0.2944.0
https://chromium.googlesource.com/chromium/src/+log/3d074282..48f434bf?pretty=fuller
Suspecting r436655 "[Extensions] Extension Port Ids and Initialization 2.0" as the only extensions-related change.

This is the expected behavior.

chrome.runtime.sendMessage should not trigger chrome.runtime.onMessage in the same window. This used to not be consistently followed (for a detailed comparison, see https://bugzilla.mozilla.org/show_bug.cgi?id=1286124#c10), but that was fixed with  bug 597698 .

If you want to trigger events in the same page, use DOM events (addEventListener + CustomEvent + dispatchEvent) or a custom event emitter library.

Thanks for clarification.

In my extension I want messages to be delivered in every frame of extension, including the sender's frame, can I rely on Chrome version to predict sendMessage behaviour? For example:

- Chrome version < 57, use only sendMessage to deliver messages to all frames
- Chrome version >= 57, use sendMessage to deliver a message to different frames and some logic to deliver the message to the current frame

#3 Even before version 57 you cannot rely on the message being triggered in the sender's frame. For even more details on when onMessage is not triggered, see https://bugzilla.mozilla.org/show_bug.cgi?id=1286124#c35

If there are always two or more extension frames (e.g. an extension page with one iframe), then what you are describing would work. In coding the logic, I suggest to assume that the browser behaves as documented, unless they are using Chrome < 57.