GitLab

* IWYU
* Eliminate using declarations via explicit qualifiers
* Replace deprecated DISALLOW_COPY_AND_ASSIGN macro
* Replace explicit GetClassName() override with View metadata macros
* Prefer file-scope constants to class-scope ones
* Declare constants as close to their use as possible, i.e. inline them
  into methods when only used once
* Comment tweaks, including removing some unhelpful or inaccurate ones,
  adding TODOs, and being more consistent
* Add utility functions CenterY(), ExecuteCommand(), UseNewWarnings()
  for common functionality.  This also results in adding a member.
* Inline ConfirmDeepScanning() and BypassDeepScanning() into their
  callers using ExecuteCommand().
* Eliminate |focus_ring_|, which is never set.
* Re-order class members in hopes of grouping related items more closely
* Set up more of |accessible_alert_timer_|'s functionality in the
  constructor and simplify the usage site as a result
* Extract a chunk of ButtonPressed() handling relating to showing an
  "open download" dialog into its own function, ShowOpenDialog(), in
  preparation for reorganizing the caller in a subsequent CL

Bug: none
Change-Id: I917ac3ab195d158fa82f5a51274b8ce5563bb15b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2304720
Commit-Queue: David Trainor <dtrainor@chromium.org>
Reviewed-by: David Trainor <dtrainor@chromium.org>
Auto-Submit: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/master@{#790171}