Plumb dst color space in many places, rather than "mode"

Plumb dst color space in many places, rather than "mode"

This is less to type in most cases, and gives us more information
(for things like picture-backed images, where we need to know all
about the destination surface).

Additionally, strip out the plumbing entirely for bitmap sources,
where we don't need to know anything.

BUG=skia:

Change-Id: I4deff6c7c345fcf62eb08b2aff0560adae4313da
Reviewed-on: https://skia-review.googlesource.com/5748
Reviewed-by: Mike Klein <mtklein@chromium.org>
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>