Factor out checkerboard function in gm and sampleapp into tools.

tools/Checkerboard.h

+/*
+ * Copyright 2015 Google Inc.

[tfarina, 2015/01/07 20:15:48]

Shouldn't this be Skia Authors rather than Google Inc.?

+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+#ifndef Checkerboard_DEFINED
+#define Checkerboard_DEFINED
+
+#include "SkColor.h"
+
+class SkCanvas;
+class SkShader;
+
+namespace sk_tools {
+
+/** Returns a newly created CheckerboardShader. */
+SkShader* CreateCheckerboardShader(SkColor c1, SkColor c2, int size);
+
+/** Draw a checkerboard pattern in the current canvas, restricted to
+    the current clip. */
+void Checkerboard(SkCanvas* canvas, SkColor color1, SkColor color2, int size);

[bsalomon, 2015/01/26 18:56:31]

lgtm, but maybe rename this function to be a bit more descriptive, e.g.
FillCheckerboard, ClearWithCheckerboard(), ...

[hal.canary, 2015/01/26 19:01:00]

DrawWithCheckerboard() ?

+
+/** A default checkerboard. */
+inline void Checkerboard(SkCanvas* canvas) {
+    Checkerboard(canvas, 0xFF999999, 0xFF666666, 8);
+}
+
+}  // namespace sk_tools
+
+#endif  // Checkerboard_DEFINED