[chromium] Expose setAutomaticallyComputeRasterScale on the WebLayer API
https://bugs.webkit.org/show_bug.cgi?id=100013

Reviewed by James Robinson.

This allows web content to opt-in to having their contentsScale
determined from their CSS transforms, without having this behaviour
unconditionally enabled globally.

Supports http://crbug.com/149943

* chromium/public/WebLayer.h:
(WebLayer):


git-svn-id: https://svn.webkit.org/repository/webkit/trunk/Source/Platform/chromium/public@132223 268f45cc-cd09-0410-ab3c-d52691b4dbfc