Convert unit tests, GMs from SkBitmapSource to SkImagesource

This removes SkBitmapSource clients within Skia.

http://crrev.com/1334173004 does the same for Blink, so we should be
able to remove SkBitmapSource in a follow-up.

R=reed@google.com,robertphillips@google.com,mtklein@google.com

Review URL: https://codereview.chromium.org/1343123002
15 files changed