Second attempt to land the integral image scaling change.

Second attempt to land the integral image scaling change.

Scale all images to the nearest rounded integer, and if there's still
any scaling factor left over, pass it on to the subsequent bilerp code.
Should avoid artifacts when tiling scaled images.

Original CL received an LGTM from reed; new version disabled tiling
in the downsamplebitmap GM; I verified that this fixes the issue
we were seeing there on non-neon androids.

BUG=skia:2888
R=reed@android.com
TBR=reed

Author: humper@google.com

Review URL: https://codereview.chromium.org/514383003