handle halfway case in scan converter

tests/DrawPathTest.cpp

Index: tests/DrawPathTest.cpp
diff --git a/tests/DrawPathTest.cpp b/tests/DrawPathTest.cpp
index 721b0304779c4b4572c5575c4653e48039316800..7f917991379db1d8e3f8f9bcb2d9044f4eae9024 100644
--- a/tests/DrawPathTest.cpp
+++ b/tests/DrawPathTest.cpp
@@ -217,6 +217,45 @@ static void test_bigcubic() {
     surface->getCanvas()->drawPath(path, paint);
 }
 
+// asserts if halfway case is not handled
+static void test_halfway() {
+    SkPaint paint;
+    SkPath path;
+    path.moveTo(16365.5f, 1394);
+    path.lineTo(16365.5f, 1387.5f);
+    path.quadTo(16365.5f, 1385.43f, 16367, 1383.96f);
+    path.quadTo(16368.4f, 1382.5f, 16370.5f, 1382.5f);
+    path.lineTo(16465.5f, 1382.5f);
+    path.quadTo(16467.6f, 1382.5f, 16469, 1383.96f);
+    path.quadTo(16470.5f, 1385.43f, 16470.5f, 1387.5f);
+    path.lineTo(16470.5f, 1394);
+    path.quadTo(16470.5f, 1396.07f, 16469, 1397.54f);
+    path.quadTo(16467.6f, 1399, 16465.5f, 1399);
+    path.lineTo(16370.5f, 1399);
+    path.quadTo(16368.4f, 1399, 16367, 1397.54f);
+    path.quadTo(16365.5f, 1396.07f, 16365.5f, 1394);
+    path.close();
+    SkPath p2;
+    SkMatrix m;
+    m.reset();
+    m.postTranslate(0.001f, 0.001f);
+    path.transform(m, &p2);
+
+    SkAutoTUnref<SkSurface> surface(SkSurface::NewRasterN32Premul(640, 480));
+    SkCanvas* canvas = surface->getCanvas();
+    canvas->translate(-16366, -1383);
+    canvas->drawPath(p2, paint);
+
+    m.reset();
+    m.postTranslate(-0.001f, -0.001f);
+    path.transform(m, &p2);
+    canvas->drawPath(p2, paint);
+
+    m.reset();
+    path.transform(m, &p2);
+    canvas->drawPath(p2, paint);
+}
+
 // we used to assert if the bounds of the device (clip) was larger than 32K
 // even when the path itself was smaller. We just draw and hope in the debug
 // version to not assert.
@@ -287,4 +326,5 @@ DEF_TEST(DrawPath, reporter) {
     test_infinite_dash(reporter);
     test_crbug_165432(reporter);
     test_big_aa_rect(reporter);
+    test_halfway();
 }