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.

R=mtklein@google.com
TBR=mtklein
NOTRY=True

Author: humper@google.com

Review URL: https://codereview.chromium.org/354193002
7 files changed