Pass the IDWriteFactory instead of relying on a global creator.

Pass the IDWriteFactory instead of relying on a global creator.

There are different variations or implementations of IDWriteFactory
with different behaviors. Allow the user to specify the factory to use.

R=scottmg@chromium.org

Committed: https://code.google.com/p/skia/source/detail?r=14000

[bungeman-skia, 2014-03-31 17:57:21]

This is an alternative to https://codereview.chromium.org/217733002/ . This is
what we already should be doing, and this avoids use of more globals.

[scottmg, 2014-03-31 18:35:32]

Thanks! lgtm for what that's worth.

(Perhaps remove sk_get_dwrite_factory from utils\win\SkDWrite so the wrong one
doesn't get used accidentally?)

[bungeman-skia, 2014-03-31 19:18:16]

Committed patchset #1 manually as r14000.