For a prototype chain foo -> global_proxy -> global_object, we used to
register a dependency from foo -> global_object. This is incorrect when
the global_proxy/global_object pairing is modified, e.g. when navigating
in iframes. With this patch, we properly register foo -> global_proxy and
global_proxy -> global_object dependencies.
Additionally, when a prototype's prototype changes from null to something
else, this new usage relation must be registered if there are other users
further down on the prototype chain that might expect a complete chain of
registrations to exist (which was the case before, and must be preserved).

BUG=chromium:571517
LOG=n
R=verwaest@chromium.org

Review URL: https://codereview.chromium.org/1559323002

Cr-Commit-Position: refs/heads/master@{#33119}