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Currently, in BridgedContentView we "opt out"[1] of BaseView's tracking area to install a different one which:
- Specifies `NSTrackingCursorUpdate`
- As a consequence, only tracks while app is active, since the docs say that always tracking is incompatible with cursor updates

However:
- Empirically, cursor updates work fine without this (some test cases: move mouse between Omnibox and other parts of topchrome, move from webcontent links/inputs to topchrome and vice-versa).
- Only tracking while app is active means we don't get entered/exited events from app switching. This means:
  - Switching away from Chrome while showing a topchrome hover tooltip keeps the hover on and makes the tooltip stuck
  - Under some circumstances, hover stops working on switching back to Chrome (see bug)
  - Even though we allow mouse clicks to function when Chrome is inactive (that is, we return `YES` from `acceptsFirstMouse:`, we don't process hovers in this case, contrary to other apps on the system.

This change removes BridgedContentView's tracking area in favor of the default one and gives BaseView some explicit enable/disables, mostly to make tests happy.

[1] By overriding a private method with a no-op!

Bug: 841792

Change-Id: Ifb5d65e22299959b8cac25a9e0a0407650a40746
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2216530Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Commit-Queue: Leonard Grey <lgrey@chromium.org>
Cr-Commit-Position: refs/heads/master@{#773848}