Revert of Revert of Fix SkTextBlob offset semantics.

Revert of Revert of Fix SkTextBlob offset semantics. (patchset #1 id:1 of https://codereview.chromium.org/609223003/)

Reason for revert:
Re-landing: Chromium-side fix to be landed with the roll (https://codereview.chromium.org/607853003/)

Original issue's description:
> Revert of Fix SkTextBlob offset semantics. (patchset #2 id:20001 of https://codereview.chromium.org/605533002/)
> 
> Reason for revert:
> Breaking the Chrome builds with the error:
> 
> [14:54:14.317833] ../../skia/ext/pixel_ref_utils.cc:221:16: error: 'drawPosText' marked 'override' but does not override any member functions
> [14:54:14.318022]   virtual void drawPosText(const SkDraw& draw,
> [14:54:14.318082]                ^
> 
> Original issue's description:
> > Fix SkTextBlob offset semantics.
> > 
> > Implement proper x/y drawTextBlob() handling by plumbing a
> > drawPosText() offset parameter (to act as an additional glyph pos
> > translation) throughout the device layer.
> > 
> > The new offset superceeds the existing constY, with a minor semantic
> > tweak: whereas previous implementations were ignoring constY in 2D
> > positioning mode (scalarsPerGlyph == 2), now the offset is always
> > observed, in all positioning modes. We can do this because existing
> > drawPosText() clients always pass constY == 0 for full positioning mode.
> > 
> > R=reed@google.com, jvanverth@google.com, robertphillips@google.com
> > 
> > Committed: https://skia.googlesource.com/skia/+/c13bc571d3e61a43b87eb97f0719abd304cafaf2
> 
> TBR=jvanverth@google.com,reed@google.com,bsalomon@google.com,fmalita@chromium.org
> NOTREECHECKS=true
> NOTRY=true
> 
> Committed: https://skia.googlesource.com/skia/+/d46b8d2bab7cfba8458432248e1568ac377429e9

TBR=jvanverth@google.com,reed@google.com,bsalomon@google.com,robertphillips@google.com
NOTREECHECKS=true
NOTRY=true

Committed: https://skia.googlesource.com/skia/+/05c4a4322e7d4f3417b7df33825bab8603d52051

[f(malita), 2014-09-29 13:28:39]

Created Revert of Revert of Fix SkTextBlob offset semantics.

[commit-bot: I haz the power, 2014-09-29 13:29:39]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/607413003/1

[commit-bot: I haz the power, 2014-09-29 13:29:57]

Committed patchset #1 (id:1) as 05c4a4322e7d4f3417b7df33825bab8603d52051