Zooms the terminal on mac with apple +/-, as that is the default behaviour for mac browsers.
Zooms the terminal on mac with apple +/-, as that is the default behaviour for mac browsers.

Change-Id: Ie686cebbef8e833d1a0094be429c94bb816b7670
Reviewed-on: https://chromium-review.googlesource.com/209882
Reviewed-by: Robert Ginda <4419ac4e35d191308e944202d542b192188656d1@chromium.org>
Tested-by: Robert Ginda <4419ac4e35d191308e944202d542b192188656d1@chromium.org>

chromium/hterm,chromium/hterm,chromium/hterm,chromium/hterm