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This is the bottom toolbar refactor to allow for 5 buttons in browsing
mode and moving the tab switcher toolbar to the bottom.

This CL breaks the old bottom toolbar MVC component into 2 components:
BrowsingModeBottomToolbar and TabSwitcherBottomToolbar. Those components
have a common root coordinator called BottomToolbarCoordinator. I've
also added two new providers. The first is the TabCountProvider. It
notifies its listeners when the tab count changes. This is useful for
the tab switcher button and the HTS tab layout icon. The other provider
is the IncognitoStateProvider. It notifies its listeners when incognito
mode is entered or exited. It also provides the tint and color for that
state.

Bug: 900759

Change-Id: Idced9f29ff4e5f3b0c6516b761416f32af78efe3

Binary-Size: Overhead from MVC
Change-Id: Idced9f29ff4e5f3b0c6516b761416f32af78efe3
Reviewed-on: https://chromium-review.googlesource.com/c/1292405
Commit-Queue: Pedro Amaral <amaralp@chromium.org>
Reviewed-by: Matthew Jones <mdjones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606604}