Reland of path ops: fix conic weight and partial coincidence

src/pathops/SkPathOpsDebug.cpp

Index: src/pathops/SkPathOpsDebug.cpp
diff --git a/src/pathops/SkPathOpsDebug.cpp b/src/pathops/SkPathOpsDebug.cpp
index a037d005713796d9e51d02720d56bf2d02777761..6dd9edd64e8a60d896bc2a9a10d70a5fcf258d34 100644
--- a/src/pathops/SkPathOpsDebug.cpp
+++ b/src/pathops/SkPathOpsDebug.cpp
@@ -402,6 +402,10 @@
     cubic[2].fX = (cubic[3].fX + cubic[2].fX * 2) / 3;
     cubic[2].fY = (cubic[3].fY + cubic[2].fY * 2) / 3;
     return cubic;
+}
+
+void SkDRect::debugInit() {
+    fLeft = fTop = fRight = fBottom = SK_ScalarNaN;
 }
 
 #include "SkOpAngle.h"
@@ -1113,7 +1117,9 @@
     if (!coin) {
         coin = this->fTop;
     }
-    SkASSERT(coin);
+    if (!coin) {
+        return;
+    }
     do {
         const SkOpPtT* startPtT = coin->fCoinPtTStart;
         const SkOpPtT* oStartPtT = coin->fOppPtTStart;