Factor out checkerboard function in gm and sampleapp into tools.

gyp/tools.gyp

Index: gyp/tools.gyp
diff --git a/gyp/tools.gyp b/gyp/tools.gyp
index 13416664fce6f4b2e2bfd070313f44dc6b23ed24..a93c78e08bb9cc5ecf1d39f98080d1831db24f46 100644
--- a/gyp/tools.gyp
+++ b/gyp/tools.gyp
@@ -106,6 +106,13 @@
       },
     },
     {
+      'target_name': 'checkerboard',
+      'type': 'static_library',
+      'sources': [ '../tools/Checkerboard.cpp', ],
+      'dependencies': [ 'skia_lib.gyp:skia_lib', ],
+      'direct_dependent_settings': { 'include_dirs': [ '../tools', ], },
+    },
+    {
       'target_name' : 'timer',
       'type': 'static_library',
       'sources': [