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This change introduces EventType and EventFlags enum types
which mirror ui::EventType and ui::EventFlags. With these,
simple mouse/touch based Mojo apps no longer have to depend
on the ui module.

Note that this doesn't introduce any keycodes. It will need
some non-trivial work which deserves its own CL.

BUG=330467
R=beng@chromium.org, darin@chromium.org, viettrungluu@chromium.org
TEST=none

Review URL: https://codereview.chromium.org/413633003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@285080 0039d316-1c4b-4281-b951-d872f2087c98