2pt conical stage for focal-pt-on-edge case

When the focal point is on the edge of the end circle, the quadratic
equation devolves to linear.  Add a stage to handle this case.

As a complication, this case can produce "degenerate" values:

 1) t == NaN
 2) R(t) < 0

For these, we're supposed to draw transparent black - which means
overwriting the color from the gradient stage.  To support this, build
a 0/1 vector mask in the context, and apply it post-gradient-stage.

Change-Id: Ice4e3243abfd8c784bb810f6c310aed7a4ac7dc8
Reviewed-on: https://skia-review.googlesource.com/21111
Commit-Queue: Florin Malita <fmalita@chromium.org>
Reviewed-by: Mike Klein <mtklein@google.com>

0 files changed, 0 insertions, 0 deletions