Speed 4: A better speed/compression compromise.
Speed 4: A better speed/compression compromise.

Before this patch, speed 4 was:
- 8% worse on lowres and 8.3% worse on midres than speed 3
- 2x faster than speed 3

With this patch, speed 4 is:
- 4.8% worse on lowres and 4.3% worse on midres than speed 3
- 1.5x faster than speed 3

BUG=aomedia:1679

Change-Id: Id066e850f042284ba19b833e7057a1d9f19e30b5

GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom