Bug 939186 - Introducing the ReflowHelper for marionette JS tests.
And a first test using it for the Dialer Keypad.
r=gaye, rik
Merge pull request #16303 from etiennesegonzac/assert-no-reflow-keypad

Bug 939186 - Introducing the ReflowHelper for marionette JS tests.
r=gaye, rik