About two years ago (September 2015) we began pausing “non-essential” Flash content smaller than 400px in width or 300px in height. Initially we included an exception to allow plugin content that was 5x5 or smaller or had an undefined size to run. In Chrome 53 we removed that exception, but left one final exception for same origin content. The exception was meant to give developers more time to transition content away from Flash, for features that are now well-supported by the web platform (e.g. clipboard access, audio streams, etc...).
Starting in Chrome 57 we plan to start experimenting with removing this final exception, and are hoping to ship it sometime in the second half of 2017 (~Chrome 60 - August). This change will soon be visible on our earlier release channels (Canary and Dev) progressing to Beta. Our intent is to give developers and users exposure to the behavior, with a significant amount of lead time (>6 months), before enabling it for all users on Stable.