Tested this issue on Windows-10 using chrome latest stable #57.0.2987.133. By adding the provided extension in the original comment observed few error saying this file is deprecated.

Reporter@ Could you please check the attached screen-shot and please confirm is this is error message displayed from your end? If yes, I am observing the same on older version of chrome #55.0.2882.0 as well.

Thanks! 

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The attached image shows the message (in red) 

To duplicate:
Load the unpacked extension from the Extensions tab
From the Extensions tab click on html/background.html link in Inspect views.

Your console output looks like it is from the html/main.html page - those are warnings from Polymer, not relevant to this issue.

You may seem some log messages starting with injecting: - those are just debug messages for injecting content scripts into any open pages.

This message in red was new for me in 57. It did not occur in 56

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Thank you for providing more feedback. Adding requester "brajkumar@chromium.org" to the cc list and removing "Needs-Feedback" label.

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

Able to reproduce on Windows 10, Ubuntu 14.04 and Mac OS 10.12 using chrome stable M57-57.0.2987.133.

Bisect Information:
=====================
Good build: 57.0.2970.0
Bad Build : 57.0.2972.0

You are probably looking for a change made after 441545 (known good), but no later than 441546 (first known bad).

Change Log URL: 
https://chromium.googlesource.com/chromium/src/+log/7d0854a8e76496275c6ce08d72a21dca270e4469..6298fc54177c7f2919fc158a3b43e7a3e08f36fe

From the above change log suspecting below change
Review URL: https://codereview.chromium.org/2379573008

jennyz@ - Could you please check whether this is caused with respect to your change, if not please help us in assigning it to the right owner.

Thanks!

jennyz@ Gentle remainder to get an update on this stable blocker issue.

Thanks,

jennyz@ Can we we target the fix before next Beta Release which would be the Pre-Stable candidate. If the bug is not critical, please feel to punt to next milestone.

FYI: RC cut @ 4.00 PM Monday 04/17.

chrome.clipboard is only made available on chromeos platform. This is by design.

jennyz@ The error message is printed in the following situation (per the originally attached example):

1. clipboard permission is NOT requested
2. NO chrome.clipboard methods are used
3. The clipboardRead and clipboardWrite ARE requested and used

clipboardRead and clipboardWrite are supported on all platforms and have been for a long time.

per the documentation:

clipboardRead is required if the extension or app uses document.execCommand('paste').

clipboardWrite indicates the extension or app uses document.execCommand('copy') or document.execCommand('cut'). This permission is required for hosted apps; it's recommended for extensions and packaged apps.

The attached example in the original post uses all three document.execCommand from above.  They all still work as expected.

The only problem is that the error message: "chrome.clipboard is not supported on this platform or manifest version" is printed to the console even though it is irrelevant and misleading.