Add support for kEmbeddedBitmapText_Flag to DirectWrite.

Add support for kEmbeddedBitmapText_Flag to DirectWrite.

R=reed@google.com

Committed: https://code.google.com/p/skia/source/detail?r=14518

[bungeman-skia, 2014-05-01 16:12:17]

Note that this also fixes a previously overlooked issue, which is that when
subpixel was disabled, the rounding happened at the rec's text size instead of
at the actual size. This effectively meant that the advance rounding was
happening before the matrix scale was applied, leading to advance widths that
could be off by quite a bit, depending on the matrix used. Most of the changed
GMs are actually a result of this fix.

[reed1, 2014-05-01 20:21:17]

lgtm

[bungeman-skia, 2014-05-01 20:39:18]

Committed patchset #3 manually as r14518 (presubmit successful).