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This change introduces a new command line flag, --polychrome, which causes
a mac_views_browser build to use the existing Cocoa UI instead of the new
Views browser UI. This involves:

1) Linking all of the Cocoa UI in when building the Views browser;
2) Resolving symbol and filename conflicts;
3) Introducing views_mode_controller::IsViewsBrowserCocoa();
4) Having BrowserWindowFactory choose which type of BrowserWindow to create
   based on the value of views_mode_controller::IsViewsBrowserCocoa()

This change also makes unit_tests build, but not any other targets - it is
likely that browser_tests does not build. The resulting mac_views_browser
*runs* but is unstable because of bug 804950, which is hard to address
without this CL being landed.

The current name is deliberately a bit silly, under the theory that we'll pick
a better one once the approach solidifies :)

Bug: 802257,804950
Change-Id: I30aaef7ed08dd11b66d59d5b816f57641bf2f209
Reviewed-on: https://chromium-review.googlesource.com/874730
Commit-Queue: Elly Fong-Jones <ellyjones@chromium.org>
Reviewed-by: Trent Apted <tapted@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#533267}