add new readPixels with direct memory parameters

BUG=skia:
R=scroggo@google.com, bsalomon@google.com, robertphillips@google.com, fmalita@google.com

Author: reed@google.com

Review URL: https://codereview.chromium.org/199413013

git-svn-id: http://skia.googlecode.com/svn/trunk@13840 2bbb7eff-a529-9590-31e7-b0007b416f81
19 files changed