handle failing pathop tests

Some tests isolated from GrShapes_arcs do not
fail gracefully, so make sure errors are properly
handled.

TBR=reed@google.com

Bug: skia:
Change-Id: Ia8c9903e64ef755ec11c398df3e5d258ca1f5f8b
Reviewed-on: https://skia-review.googlesource.com/143112
Reviewed-by: Cary Clark <caryclark@skia.org>
Commit-Queue: Cary Clark <caryclark@skia.org>
Auto-Submit: Cary Clark <caryclark@skia.org>
diff --git a/src/pathops/SkPathOpsCommon.cpp b/src/pathops/SkPathOpsCommon.cpp
index 19e80b0..c1b134f 100644
--- a/src/pathops/SkPathOpsCommon.cpp
+++ b/src/pathops/SkPathOpsCommon.cpp
@@ -156,7 +156,8 @@
                 }
                 // OPTIMIZATION: should this also add to the chase?
                 if (sortable) {
-                    (void) segment->markAngle(maxWinding, sumWinding, angle);
+                    // TODO: add error handling
+                    SkAssertResult(segment->markAngle(maxWinding, sumWinding, angle, nullptr));
                 }
             }
         }