Fix SkPath::arcTo when sweepAngle is tiny and radius is big

gm/addarc.cpp

Index: gm/addarc.cpp
diff --git a/gm/addarc.cpp b/gm/addarc.cpp
index 9280140794af70413a949847c64fde74d9171efd..8c23aa89bde1641eebeffb7da5ca1000d33e44a2 100644
--- a/gm/addarc.cpp
+++ b/gm/addarc.cpp
@@ -230,3 +230,35 @@ private:
     typedef skiagm::GM INHERITED;
 };
 DEF_GM( return new ManyArcsGM; )
+
+// Lifted from https://bugs.chromium.org/p/chromium/issues/detail?id=640031
+class TinyAngleBigRadiusArcsGM : public skiagm::GM {
+public:
+    TinyAngleBigRadiusArcsGM() {}
+
+protected:
+    SkString onShortName() override { return SkString("tinyanglearcs"); }
+
+    SkISize onISize() override { return SkISize::Make(620, 330); }
+
+    void onDraw(SkCanvas* canvas) override {
+        SkPaint paint;
+        paint.setAntiAlias(true);
+        paint.setStyle(SkPaint::kStroke_Style);
+
+        canvas->translate(10, 10);
+
+        SkPath path;
+        path.moveTo(50, 20);
+        path.lineTo(50, 0);
+        // A combination of tiny sweepAngle + large radius, we should draw a line.
+        html_canvas_arc(&path, 50, 100000, 100000, 270, 270 - 0.00572957795,
+                        false);
+        path.lineTo(60, 20);
+        canvas->drawPath(path, paint);
+    }
+
+private:
+    typedef skiagm::GM INHERITED;
+};
+DEF_GM( return new TinyAngleBigRadiusArcsGM; )