Revert of Keep track in the browser of which frames have onunload and onbeforeunload handlers.

Revert of Keep track in the browser of which frames have onunload and onbeforeunload handlers. (patchset #10 id:180001 of https://codereview.chromium.org/2783723002/ )

Reason for revert:
Creating a revert patchset for testing. Will not be submitted.

Original issue's description:
> Keep track in the browser of which frames have onunload and onbeforeunload handlers.
> 
> This allows PlzNavigate to only pause fetching the request if it knows that the page has an onbeforeunload handler, where today it currently always goes to the renderer. This avoids delaying the network requests in the 95% cases that don't onbeforeunload handler on a process hop to the renderer.
> 
> BUG=365039, 705559
> CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_site_isolation
> R=dcheng@chromium.org, nasko@chromium.org
> 
> Review-Url: https://codereview.chromium.org/2783723002 .
> Cr-Commit-Position: refs/heads/master@{#460581}
> Committed: https://chromium.googlesource.com/chromium/src/+/a2c84a7664eceb5cbeaae5bf1ec32da0060e3097

TBR=nasko@chromium.org,dcheng@chromium.org,jam@chromium.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=365039, 705559

[achuithb, 2017-04-05 17:40:44]

Created Revert of Keep track in the browser of which frames have onunload and
onbeforeunload handlers.