Add gpu fast path for two point conical gradients.

Also shader changes should help numerical issues on certain android gpus

BUG=179264
R=bsalomon@google.com

Author: egdaniel@google.com

Review URL: https://codereview.chromium.org/238443006

git-svn-id: http://skia.googlecode.com/svn/trunk@14316 2bbb7eff-a529-9590-31e7-b0007b416f81
4 files changed