Add dash lines batch unit test

src/gpu/GrTestUtils.cpp

Index: src/gpu/GrTestUtils.cpp
diff --git a/src/gpu/GrTestUtils.cpp b/src/gpu/GrTestUtils.cpp
index afd9fd80b6787a5f010d965e932e6205907afda8..d0cea5565ce9c2c39af51b7b06ec08526980ec29 100644
--- a/src/gpu/GrTestUtils.cpp
+++ b/src/gpu/GrTestUtils.cpp
@@ -29,6 +29,32 @@ const SkMatrix& TestMatrix(SkRandom* random) {
     return gMatrices[random->nextULessThan(static_cast<uint32_t>(SK_ARRAY_COUNT(gMatrices)))];
 }
 
+const SkMatrix& TestMatrixPreservesRightAngles(SkRandom* random) {
+    static SkMatrix gMatrices[4];
+    static bool gOnce;
+    if (!gOnce) {
+        // identity
+        gMatrices[0].reset();
+        // translation
+        gMatrices[1].setTranslate(SkIntToScalar(-100), SkIntToScalar(100));
+        // scale
+        gMatrices[2].setScale(SkIntToScalar(17), SkIntToScalar(17));
+        // scale + translation
+        gMatrices[3].setScale(SkIntToScalar(-17), SkIntToScalar(-17));
+        gMatrices[3].postTranslate(SkIntToScalar(66), SkIntToScalar(-33));
+        // orthogonal basis vectors
+        gMatrices[4].reset();
+        gMatrices[4].setScale(SkIntToScalar(-1), SkIntToScalar(-1));
+        gMatrices[4].setRotate(47);

[brucedawson, 2015/04/30 20:19:06]

These three lines of code reference gMatrices[4] but the last legal offset is
gMatrices[3]. This was detected through a /analyze warning that said:

third_party\skia\src\gpu\grtestutils.cpp(46) : warning C6200: Index '4' is out
of valid index range '0' to '3' for non-stack buffer 'class SkMatrix * `class
SkMatrix const & __cdecl GrTest::TestMatrixPreservesRightAngles(class SkRandom
*)'::`2'::gMatrices'.

+        gOnce = true;
+
+        for (size_t i = 0; i < SK_ARRAY_COUNT(gMatrices); i++) {
+            SkASSERT(gMatrices[i].preservesRightAngles());
+        }
+    }
+    return gMatrices[random->nextULessThan(static_cast<uint32_t>(SK_ARRAY_COUNT(gMatrices)))];
+}
+
 const SkRect& TestRect(SkRandom* random) {
     static SkRect gRects[1];
     static bool gOnce;