google-chromemacos
After upgrading to Yosemite, I found there are quite some Google Chrome Helper (not responding) processes after MacBook resumes from hibernate (closing the MacBook cover).
It seems to me close-and-reopen Chrome will clean up the (Not Responding) processes.
What is the problem?
This bug is fixed on Oct 31, 2013 (#89 thakis@chromium.org)
and the fix will reach the stable channel eventually.
This is an issue with how Activity Monitor determines responsiveness – these processes are running perfectly fine.
(We changed chrome to work around that Activity Monitor issue, and the fix will reach you eventually, depending on which channel you use, how far we merge this, etc.)
Google Chrome Helper instances are used for various plugins you may have installed. Unless a plugin is glitchy or doesn't play nice with other plugins, there is generally no problem having some or many Chrome Helper processes running.
This Wired article explains a bit about Chrome Helper.
Best Answer
You can see developers from the Google Chrome team discussing the issue here.
If I'm reading correctly, something triggers a change in the way things are drawn to the screen. The WindowServer process, which is responsible for drawing everything to the screen, issues a notification announcing that change to every process with a GUI and expects an acknowledgement of the notification. These Chrome processes don't respond, so the operating system flags the processes as "Not responding".
Long story short is that they think this is just a cosmetic problem that will be fixed shortly. It doesn't actually seem to affect performance.
They've found and fixed similar issues in the past, for example 304860. I think this is a side-effect of the multi-process architecture that they use for Chrome.