GitLab

 - Move GenericHandler from content/ to chrome/
 - Rename to NavigationHandler
 - Stop registering it blindly for all WebUI pages within WebContentsImpl.
 - Register it explicitly in HistoryUI, the only currently known usage of
   it.
 - Change util.js so that a call to listenForPrivilegedLinkClicks() is
   required to trigger that functionality. Previously listeners were added
   as soon as util.js was evaluated.

Note there are probably a few more places that use NavigationHandler to be
registered. The goal of this CL is to narrow down who needs this functionality
and explicitly add it there. So some temporary regressions are expected.

Bug: 1020360
Change-Id: I2e2f5a0fe06cb8268a38380f29547afa94e7450c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1894911
Commit-Queue: Demetrios Papadopoulos <dpapad@chromium.org>
Reviewed-by: Dan Beam <dbeam@chromium.org>
Reviewed-by: Nasko Oskov <nasko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#712251}