Cherry-pick: cc: fix content_to_screen_scale in UpdateTilePriorities.

Cherry-pick with conflict of chromium crrev.com/290074

Conflicts:
	cc/resources/picture_layer_tiling.cc

BUG: 17303244
Change-Id: Ibbef79ee10c3a7b9abfec80b476092b7465e6417
2 files changed