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This CL adds a helper interface for ui controls that will be used
by Ozone/Linux (maybe by others as well in the future) when
interactive_ui_tests are run.

We need a way to send emulated events through platform specific
methods. For example, XSendEvent in case of X11 and libei library
in case of Wayland (though, this library is under development and
we need to figure out short term and long term solution. Probably,
the short term solution will be injecting ui::Events directly
into Ozone/Wayland and the long term one is libei).

In this CL, ui_test_support is added for Ozone. views is the only
component allowed to depend on that. Also, a factory to create
OzoneUIControlsTestHelper is added. Actually, the factory methods
are generated the same way as the methods for pixmap factory or
ozone platform factory. Also, stub is added so that it's clear
if the platform doesn't support OzoneUIControlsTestHelper or
doesn't have it implemented.

Please note that in order to generate the factory methods, I had
to make platform_object.h public. Alternatively, it might be
moved into a separate source_set so that ozone gn targets that
need that can depend on that directly.

More details at https://docs.google.com/document/d/1K3zyatrNrlm7XRzkZ2I9tJqVh5dNbT3obcw-JW9SUE4

Actual implementation for Ozone/X11 (at least this one) will be
added in a follow up cl.

Bug: 1134495
Change-Id: Ia7753b9f0fc329799d4ada638dcae02bac604405
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2445110
Commit-Queue: Maksim Sisov (GMT+3) <msisov@igalia.com>
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Robert Kroeger <rjkroege@chromium.org>
Cr-Commit-Position: refs/heads/master@{#814181}