Factor out checkerboard function in gm and sampleapp into tools.

gm/imagefiltersscaled.cpp

Index: gm/imagefiltersscaled.cpp
diff --git a/gm/imagefiltersscaled.cpp b/gm/imagefiltersscaled.cpp
index 8b44bd0563bab0c7350db35c0db05b877e75ed09..9cb4739a377d911f30c47cb1322ad215abbfd3f6 100644
--- a/gm/imagefiltersscaled.cpp
+++ b/gm/imagefiltersscaled.cpp
@@ -5,6 +5,7 @@
  * found in the LICENSE file.
  */
 
+#include "checkerboard.h"
 #include "gm.h"
 #include "SkColor.h"
 #include "SkBitmapSource.h"
@@ -43,27 +44,6 @@ protected:
         return SkISize::Make(1428, 500);
     }
 
-    void make_checkerboard() {
-        fCheckerboard.allocN32Pixels(64, 64);
-        SkCanvas canvas(fCheckerboard);
-        canvas.clear(0x00000000);
-        SkPaint darkPaint;
-        darkPaint.setColor(0xFF404040);
-        SkPaint lightPaint;
-        lightPaint.setColor(0xFFA0A0A0);
-        for (int y = 0; y < 64; y += 16) {
-          for (int x = 0; x < 64; x += 16) {
-            canvas.save();
-            canvas.translate(SkIntToScalar(x), SkIntToScalar(y));
-            canvas.drawRect(SkRect::MakeXYWH(0, 0, 8, 8), darkPaint);
-            canvas.drawRect(SkRect::MakeXYWH(8, 0, 8, 8), lightPaint);
-            canvas.drawRect(SkRect::MakeXYWH(0, 8, 8, 8), lightPaint);
-            canvas.drawRect(SkRect::MakeXYWH(8, 8, 8, 8), darkPaint);
-            canvas.restore();
-          }
-        }
-    }
-
     void make_gradient_circle(int width, int height) {
         SkScalar x = SkIntToScalar(width / 2);
         SkScalar y = SkIntToScalar(height / 2);
@@ -85,7 +65,10 @@ protected:
 
     virtual void onDraw(SkCanvas* canvas) {
         if (!fInitialized) {
-            this->make_checkerboard();
+            fCheckerboard.allocN32Pixels(64, 64);
+            SkCanvas checkerboardCanvas(fCheckerboard);
+            skiagm::Checkerboard(&checkerboardCanvas, 0xFFA0A0A0, 0xFF404040);
+
             this->make_gradient_circle(64, 64);
             fInitialized = true;
         }