When filling nested rect path check for empty inner and empty outer rects

tests/skbug5221.cpp

+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "Test.h"
+#include "SkCanvas.h"
+#include "SkSurface.h"
+
+// This passes by not crashing.
+static void test(SkCanvas* canvas) {
+    SkPaint paint;
+    paint.setAntiAlias(true);
+    canvas->scale(63, 0);
+    static const char kTxt[] = "A";
+    canvas->drawText(kTxt, SK_ARRAY_COUNT(kTxt), 50, 50, paint);
+}
+
+DEF_TEST(skbug5221, r) {
+    sk_sp<SkSurface> surface(SkSurface::MakeRaster(SkImageInfo::MakeN32Premul(256, 256)));
+    test(surface->getCanvas());
+}
+
+#if SK_SUPPORT_GPU
+DEF_GPUTEST_FOR_ALL_CONTEXTS(skbug5221_GPU, r, contextInfo) {
+    sk_sp<SkSurface> surface(SkSurface::MakeRenderTarget(contextInfo.fGrContext, SkBudgeted::kYes,
+                                                         SkImageInfo::MakeN32Premul(256, 256), 0,
+                                                         nullptr));
+    test(surface->getCanvas());
+}
+#endif