Factor out checkerboard function in gm and sampleapp into tools.

gyp/SampleApp.gyp

 #
 {
   'variables': {
     #manually set sample_pdf_file_viewer to 1 to have the PdfViewer in SampleApp
     'sample_pdf_file_viewer%': 0,
   },
   'targets': [
     {
       'target_name': 'SampleApp',
       'type': 'executable',
@@ skipping 134 matching lines @@
       'dependencies': [
         'animator.gyp:animator',
         'etc1.gyp:libetc1',
         'experimental.gyp:experimental',
         'flags.gyp:flags',
         'lua.gyp:lua',
         'pdf.gyp:pdf',
         'skia_lib.gyp:skia_lib',
         'tools.gyp:resources',
         'tools.gyp:sk_tool_utils',
+        'tools.gyp:checkerboard',
         'views.gyp:views',
         'views_animated.gyp:views_animated',
         'xml.gyp:xml',
       ],
      'conditions' : [
        [ 'sample_pdf_file_viewer == 1', {
          'defines': [
            'SAMPLE_PDF_FILE_VIEWER',
          ],
          'dependencies': [
@@ skipping 137 matching lines @@
         }],
       ],
       'msvs_settings': {
         'VCLinkerTool': {
           'SubSystem': '2',
         },
       },
     },
   ],
 }