Scale 3x3 block instead of 16x16 block in each loop. Disabled by
default.

Benefits:
1. Reduced number of different phase_scaler from 16 to 3.
   Optimization code will be smaller and faster.
2. Maximum phase_scaler drifting will be reduced from 5/16 to 1/24.
   (The drifting is 1/(3*16) in each step.)

BUG=webm:1419

Change-Id: I59a1f7496d89a1b090498c935d30cfcf1d0c282b