More distance field improvements

More distance field improvements:
- Make sure we only use the 0,0 subpixel glyph
- Copy image data into outsized buffer to ensure we capture outer edges
- Change edge dump to blend better with original glyph
- Edges are detected across >128 and <128 boundaries, or when
  there are two non-zero <128 pixels next to each other

BUG=skia:

Committed: http://code.google.com/p/skia/source/detail?r=13916

[robertphillips, 2014-03-24 14:32:28]

lgtm

https://codereview.chromium.org/208893003/diff/20001/src/core/SkDistanceField...
File src/core/SkDistanceFieldGen.cpp (right):

https://codereview.chromium.org/208893003/diff/20001/src/core/SkDistanceField...
src/core/SkDistanceFieldGen.cpp:359: unsigned char* copyPtr = (unsigned char*)
copyStorage.get();
Wouldn't it be cheaper to zero the top and bottom rows then just handle the
first and last bytes on each line individually?

[jvanverth1, 2014-03-24 17:18:03]

https://codereview.chromium.org/208893003/diff/20001/src/core/SkDistanceField...
File src/core/SkDistanceFieldGen.cpp (right):

https://codereview.chromium.org/208893003/diff/20001/src/core/SkDistanceField...
src/core/SkDistanceFieldGen.cpp:359: unsigned char* copyPtr = (unsigned char*)
copyStorage.get();
On 2014/03/24 14:32:28, robertphillips wrote:
> Wouldn't it be cheaper to zero the top and bottom rows then just handle the
> first and last bytes on each line individually?

Done.

[jvanverth1, 2014-03-24 17:18:11]

The CQ bit was checked by jvanverth@google.com

[commit-bot: I haz the power, 2014-03-24 17:18:12]

CQ is trying da patch. Follow status at
https://skia-tree-status.appspot.com/cq/jvanverth@google.com/208893003/40001

[commit-bot: I haz the power, 2014-03-24 18:34:07]

Change committed as 13916