Chrome Version: (copy from chrome://version)
OS: (e.g. Win7, OSX 10.9.5, etc...)

What steps will reproduce the problem?
(1) Run a Debug trunk build with --site-per-process.
(2) Visit Youtube.com
(3)

What is the expected result?
Watch cat videos.

What happens instead?
Renderer crashes:
[1:1:1211/105409.439419:FATAL:PaintLayer.cpp(2735)] Check failed: IsAllowedToQueryCompositingState(). 


The crash stack is similar to the one in issue 792687, but we are hitting the problem through a different vector. Youtube is loading an ad that embeds Youtube again, so we are creating the 'A embeds B embeds A' scenario that I mentioned here https://bugs.chromium.org/p/chromium/issues/detail?id=792687#c20.

I'll see if fixing the incorrect use of mainFrame()->IsLocalFrame() fixes the problem.