This allows more consistent and efficient conversion between the
two types.

Because we're including the header for SkColorSpace, targets that
include this can't play fast and loose with dependencies. Break off
the color space dependencies as //ui/gfx:color_space, and include
it in the media and remoting BUILD.gn that need it.

BUG=634102
CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_trusty_blink_rel

Review-Url: https://codereview.chromium.org/2598833002
Cr-Commit-Position: refs/heads/master@{#440747}