Use vertex attributes for dash effect in gpu

This will allow us to batch dashed lines together when drawing. Also, this removes the need for
a coord transform matrix in the shader, thus we save the cost of uploading a new matrix uniform
everytime we do a simple transform to the dashed line we are drawing.

BUG=skia:
R=bsalomon@google.com

Author: egdaniel@google.com

Review URL: https://codereview.chromium.org/326103002
10 files changed