Set ambient stroke to full width of blur.

Gives better blur behavior around corners and looks more like an
actual blur. Also removed the color members, as they're mostly
constant.

Bug: skia:7971
Change-Id: I22a5dcb93da1f39040148ca6ddb391844382cc73
Reviewed-on: https://skia-review.googlesource.com/153280
Commit-Queue: Jim Van Verth <jvanverth@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
6 files changed