Cherry pick two CLs back to M39 to fix a bug

Bug fix for cull_line in SkDashPathEffect.
Review URL: https://codereview.chromium.org/703783002

Crop the fast path dashed lines to the cull rect
Review URL: https://codereview.chromium.org/699623003
BUG=428296
R=bsalomon@google.com

Review URL: https://codereview.chromium.org/706013005