Refactor bitmap scaler to make it easier to migrate rest of chrome to use it

Refactor bitmap scaler to make it easier to migrate rest of chrome to use it

Previously, the set of platform-specific function pointers to do fast convolution (e.g., neon, SSE) were passed in a structure to the scaler.

I refactored this so that the scaler fills in these function pointers after it's called, so the caller doesn't have to worry about it.

TBR=mtklein
NOTRY=True

Committed: https://skia.googlesource.com/skia/+/4f96ab36180489748f4e9bb249d773414ef0d6cb

[humper, 2014-06-27 17:49:51]

The CQ bit was checked by humper@google.com

[commit-bot: I haz the power, 2014-06-27 17:50:45]

CQ is trying da patch. Follow status at
 https://skia-tree-status.appspot.com/cq/humper@google.com/354193002/1

[humper, 2014-06-27 18:26:43]

The CQ bit was unchecked by humper@google.com

[humper, 2014-06-27 18:26:46]

The CQ bit was checked by humper@google.com

[commit-bot: I haz the power, 2014-06-27 18:26:58]

CQ is trying da patch. Follow status at
 https://skia-tree-status.appspot.com/cq/humper@google.com/354193002/1

[commit-bot: I haz the power, 2014-06-27 18:27:07]

Change committed as 4f96ab36180489748f4e9bb249d773414ef0d6cb