optimize pathops coverage

Remove unused code from SkOpSegment.cpp and friends.
Add new tests exposed by coverage.
Fix a bug exposed by coverage -- removing the need to detect points that are nearby when intersecting.
Add gyp rule for building coverage flavor on Mac.

R=mtklein@google.com

Author: caryclark@google.com

Review URL: https://codereview.chromium.org/75453003

git-svn-id: http://skia.googlecode.com/svn/trunk@12344 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/pathops/SkAddIntersections.cpp b/src/pathops/SkAddIntersections.cpp
index 7d5fc0d..035a50e 100644
--- a/src/pathops/SkAddIntersections.cpp
+++ b/src/pathops/SkAddIntersections.cpp
@@ -397,8 +397,8 @@
                 SkASSERT(ts[0][pt] >= 0 && ts[0][pt] <= 1);
                 SkASSERT(ts[1][pt] >= 0 && ts[1][pt] <= 1);
                 SkPoint point = ts.pt(pt).asSkPoint();
-                int testTAt = wt.addT(wn, point, ts[swap][pt], swap && ts.isNear(pt));
-                int nextTAt = wn.addT(wt, point, ts[!swap][pt], !swap && ts.isNear(pt));
+                int testTAt = wt.addT(wn, point, ts[swap][pt]);
+                int nextTAt = wn.addT(wt, point, ts[!swap][pt]);
                 wt.addOtherT(testTAt, ts[!swap][pt], nextTAt);
                 wn.addOtherT(nextTAt, ts[swap][pt], testTAt);
             }
@@ -425,7 +425,7 @@
         SkASSERT(ts[1][0] >= 0 && ts[1][0] <= 1);
         SkPoint point = ts.pt(0).asSkPoint();
         int testTAt = wt.addSelfT(wt, point, ts[0][0]);
-        int nextTAt = wt.addT(wt, point, ts[1][0], ts.isNear(0));
+        int nextTAt = wt.addT(wt, point, ts[1][0]);
         wt.addOtherT(testTAt, ts[1][0], nextTAt);
         wt.addOtherT(nextTAt, ts[0][0], testTAt);
     } while (wt.advance());