LocalFrameView has boolean values for hidden_for_throttling_ and subtree_throttled_, which to support OOPIFs are being similarly replicated to RemoteFrameView, and plumbed through various classes in the browser process to transport them. It would be nicer to be passing a flag word with clear constants to prevent confusion in working with methods with signatures resembling "UpdateThrottling(bool, bool)"

This was suggested during review of an OOPIF throttling CL: https://chromium-review.googlesource.com/c/chromium/src/+/719601