harden and speed up path op unit tests

tests/PathOpsDVectorTest.cpp

Index: tests/PathOpsDVectorTest.cpp
diff --git a/tests/PathOpsDVectorTest.cpp b/tests/PathOpsDVectorTest.cpp
index 6d752c53880d07c0d1e7954b6525878478a1d57e..23ca2a818635199dd0ece8940a2e08d0af1d7f07 100644
--- a/tests/PathOpsDVectorTest.cpp
+++ b/tests/PathOpsDVectorTest.cpp
@@ -4,6 +4,7 @@
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
+#include "PathOpsTestCommon.h"
 #include "SkPathOpsPoint.h"
 #include "Test.h"
 
@@ -22,7 +23,9 @@ static const size_t tests_count = SK_ARRAY_COUNT(tests);
 static void PathOpsDVectorTest(skiatest::Reporter* reporter) {
     for (size_t index = 0; index < tests_count - 1; ++index) {
         SkDVector v1 = tests[index + 1] - tests[index];
+        SkASSERT(ValidVector(v1));
         SkDVector v2 = tests[index] - tests[index + 1];
+        SkASSERT(ValidVector(v2));
         v1 += v2;
         REPORTER_ASSERT(reporter, v1.fX == 0 && v1.fY == 0);
         SkDPoint p = tests[index + 1] + v2;