Fix pinchUpdate scale semantics

Fix pinchUpdate scale semantics

We expect the 'scale' value for GesturePinchUpdate to be a scale factor
(with 1.0 meaning no scaling).  The Cocoa API docs say you must add
1.0 to the magnification value to get the scale factor.

BUG=289887
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=172763

[Rick Byers, 2014-04-25 21:07:15]

Adam, please take a look.

I originally planned on fixing this via an ugly 5-sided patch between blink and
chromium.  But trackpad pinch is a little used feature, I think it's better to
just fix chromium and blink about the same time (no tests will fail since we
only have unit-level coverage).  Worst case if we have a canary build where
trackpad pinch-zoom is busted I think that's fine.

Corresponding chromium change is here:
https://codereview.chromium.org/255843004/

[abarth-chromium, 2014-04-25 22:19:58]

LGTM assuming the chromium side contains a test.

[Rick Byers, 2014-04-28 13:28:49]

The CQ bit was checked by rbyers@chromium.org

[commit-bot: I haz the power, 2014-04-28 13:29:11]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/rbyers@chromium.org/254783004/1

[commit-bot: I haz the power, 2014-04-28 14:39:42]

Change committed as 172763