Factor out checkerboard function in gm and sampleapp into tools.

samplecode/SampleColorFilter.cpp

Index: samplecode/SampleColorFilter.cpp
diff --git a/samplecode/SampleColorFilter.cpp b/samplecode/SampleColorFilter.cpp
index fb5d42744f2a502b6ff5265f932f1c906e59fcef..175f724710a1f48bd84efba346d698b367e2fa0d 100644
--- a/samplecode/SampleColorFilter.cpp
+++ b/samplecode/SampleColorFilter.cpp
@@ -5,6 +5,7 @@
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
+#include "Checkerboard.h"
 #include "SampleCode.h"
 #include "SkView.h"
 #include "SkCanvas.h"
@@ -84,20 +85,6 @@ static void test_5bits() {
     SkDebugf("--- trunc: %d %d  round: %d %d new: %d %d\n", e0, ae0, e1, ae1, e2, ae2);
 }
 
-// No longer marked static, since it is externed in SampleUnpremul.
-SkShader* createChecker();
-SkShader* createChecker() {
-    SkBitmap bm;
-    bm.allocN32Pixels(2, 2);
-    bm.lockPixels();
-    *bm.getAddr32(0, 0) = *bm.getAddr32(1, 1) = SkPreMultiplyColor(0xFFFFFFFF);
-    *bm.getAddr32(0, 1) = *bm.getAddr32(1, 0) = SkPreMultiplyColor(0xFFCCCCCC);
-    SkMatrix m;
-    m.setScale(12, 12);
-    return SkShader::CreateBitmapShader(bm, SkShader::kRepeat_TileMode,
-                                        SkShader::kRepeat_TileMode, &m);
-}
-
 static SkBitmap createBitmap(int n) {
     SkBitmap bitmap;
     bitmap.allocN32Pixels(n, n);
@@ -131,7 +118,8 @@ class ColorFilterView : public SampleView {
 public:
     ColorFilterView() {
         fBitmap = createBitmap(N);
-        fShader = createChecker();
+        fShader = sk_tools::CreateCheckerboardShader(
+                0xFFCCCCCC, 0xFFFFFFFF, 12);
 
         if (false) { // avoid bit rot, suppress warning
             test_5bits();