mojo events: Add |screen_location| to LocationData.

mojo events: Add |screen_location| to located events.

Building blink events requires more data than we currently pass through
mojo::EventPtr. That data is available on the side that has the
base::NativeEvent, so we now send both the view relative location and
the system location through. This also lets us drop a DEPS on "ui/events"
from the html viewer.

Eventually, we'll want our own event types, but this works for now.

BUG=403514
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=290077

[Ben Goodger (Google), 2014-08-15 21:41:15]

lgtm

[Elliot Glaysher, 2014-08-15 21:47:36]

The CQ bit was checked by erg@chromium.org

[commit-bot: I haz the power, 2014-08-15 21:49:54]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/erg@chromium.org/478523002/100001

[commit-bot: I haz the power, 2014-08-16 01:11:19]

Committed patchset #6 (100001) as 290077