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 b419187ffff37be31cad7d4eeaaaae7b62d6f2df..084de00fbe5afe13ffb9167719ff94fd457e2d9b 100644
--- a/gm/imagefiltersscaled.cpp
+++ b/gm/imagefiltersscaled.cpp
@@ -5,20 +5,21 @@
  * found in the LICENSE file.
  */
 
-#include "gm.h"
-#include "SkColor.h"
+#include "Checkerboard.h"
 #include "SkBitmapSource.h"
 #include "SkBlurImageFilter.h"
+#include "SkColor.h"
 #include "SkDisplacementMapEffect.h"
 #include "SkDropShadowImageFilter.h"
 #include "SkGradientShader.h"
 #include "SkLightingImageFilter.h"
+#include "SkMatrixImageFilter.h"
 #include "SkMorphologyImageFilter.h"
 #include "SkOffsetImageFilter.h"
 #include "SkPerlinNoiseShader.h"
 #include "SkRectShaderImageFilter.h"
-#include "SkMatrixImageFilter.h"
 #include "SkScalar.h"
+#include "gm.h"
 
 #define RESIZE_FACTOR SkIntToScalar(4)
 
@@ -40,27 +41,6 @@ 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);
@@ -82,7 +62,10 @@ protected:
 
     virtual void onDraw(SkCanvas* canvas) {
         if (!fInitialized) {
-            this->make_checkerboard();
+            fCheckerboard.allocN32Pixels(64, 64);
+            SkCanvas checkerboardCanvas(fCheckerboard);
+            sk_tools::DrawCheckerboard(&checkerboardCanvas, 0xFFA0A0A0, 0xFF404040, 8);
+
             this->make_gradient_circle(64, 64);
             fInitialized = true;
         }