Prevent scrolling in top-level window while dialog is open

Because scroll events cannot be canceled or prevented from bubbling
up, the only way to prevent the scrolling is to cancel the actual key
and mouse wheel events.

PhantomJs -= 2

Change-Id: I540738459181c37d11caf5db07345703e7000ef9
Merge "Prevent scrolling in top-level window while dialog is open"