Fix subpixel font scaling for DirectWrite

Fix subpixel font scaling for DirectWrite

Implement support for subpixel font scaling for the Windows DirectWrite
backend and change how the subpixel flag is set to use the SkPaint::
kSubpixelText_Flag flag instead of the method as otherwise the setFlags
call clears the subpixel flag.

BUG=25541
R=leviw@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=171817

[eae, 2014-04-16 22:44:14]

On 2014/04/16 22:36:16, eae wrote:

Image diffs: 
https://storage.googleapis.com/chromium-layout-test-archives/win_blink_rel/41...

[leviw_travelin_and_unemployed, 2014-04-16 22:48:00]

On 2014/04/16 22:44:14, eae wrote:
> On 2014/04/16 22:36:16, eae wrote:
> 
> Image diffs: 
>
https://storage.googleapis.com/chromium-layout-test-archives/win_blink_rel/41...

Code change looks great, but I did find one test that's failing:
virtual/windows-directwrite/fast/text/shaping/shaping-selection-rect.html

[eae, 2014-04-16 22:52:34]

> Code change looks great, but I did find one test that's failing:
> virtual/windows-directwrite/fast/text/shaping/shaping-selection-rect.html

Good catch. Marked as broken and added to my TODO list.

PTAL

[leviw_travelin_and_unemployed, 2014-04-16 22:58:38]

lgtm

[commit-bot: I haz the power, 2014-04-16 22:59:33]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/eae@chromium.org/239283010/20001

[commit-bot: I haz the power, 2014-04-16 23:59:27]

Change committed as 171817