Make image resolution more strict, clean gallery pubspec.yaml (#17241) - #17322

We found a Contributor License Agreement for you (the sender of this pull request), but were unable to find agreements for all the commit author(s) or Co-authors. If you authored these, maybe you used a different email address in the git commits than was used to sign the CLA (login here to double check)? If these were authored by someone else, then they will need to sign a CLA as well, and confirm that they're okay with these being contributed to Google.
In order to pass this check, please resolve this problem and have the pull request author add another comment and the bot will run again. If the bot doesn't comment, it means it doesn't think anything has changed.

I have no idea who the other "contributor" for this patch is. It sounds like my local git is picking a stale alternative github account I may have used in the past.

CLAs look good, thanks!

@HansMuller This appveyor error is very interesting, I have no idea what to do next. My guess is that running it again may work:

FileSystemException: Deletion failed, path = 'C:\Users\appveyor\AppData\Local\Temp\1\analyze_sample_code_86ff9924-5516-11e8-81e7-00155d57f4bf' (OS Error: The process cannot access the file because it is being used by another process.

Sorry, that looks like a build flake. I've restarted the AppVeyor bot

@HansMuller all green on CI 👍