Whenever the add-on shims wrap an object, they first compute its "object tag". They really just do a few instanceof checks to see if it's a XUL node, a window, a docshell, or whatever. In particular, when the object is a CPOW, we do two instanceof checks. Each one sends a sync IPC message. Like in bug 1091964, this information is constant for a given object. So this patch just sends the tag along with the CPOW, same as in bug 1091964. I had to make a new interface for doing this. This patch reduces the number of CPOW IPCs we do on my testcase from 16837 to 8100.

Comment on attachment 8514716 [details] [diff] [review] cache-obj-tag Review of attachment 8514716 [details] [diff] [review]: ----------------------------------------------------------------- ::: js/xpconnect/idl/xpccomponents.idl @@ +441,5 @@ > + * nsIRemoteTagService.getRemoteObjectTag method. It's sent along > + * with the CPOW to the remote process, where it can be fetched > + * with this function, getCrossProcessWrapperTag. > + */ > + ACString getCrossProcessWrapperTag(in jsval obj); Need to bump the IID.

sorry had to back this out in https://treeherder.mozilla.org/ui/#/jobs?repo=mozilla-inbound&revision=541dc2f509e2 since of this changes seems to have caused test failures like https://treeherder.mozilla.org/ui/logviewer.html#?job_id=3605040&repo=mozilla-inbound

The rooting hazards that this patch was implicated in did not go away after the backout. Relanding. https://hg.mozilla.org/integration/mozilla-inbound/rev/c97553c13fb6