Factor out checkerboard function in gm and sampleapp into tools.

expectations/gm/Test-Ubuntu12-ShuttleA-GTX660-x86-Release/expected-results.json

 {
   "actual-results": {
     "failed": null, 
     "failure-ignored": null, 
     "no-comparison": null, 
     "succeeded": null
   }, 
   "expected-results": {
     "3x3bitmaprect_565.png": {
       "allowed-digests": [
@@ skipping 6002 matching lines @@
       ], 
       "reviewed-by-human": true
     }, 
     "colorwheel_pdf-poppler.png": {
       "allowed-digests": [
         [
           "bitmap-64bitMD5", 
           9105323639568114333
         ]
       ], 
-      "bugs": [
-        3180
-      ], 
+      "ignore-failure": true,
       "reviewed-by-human": true
     }, 
     "colorwheelnative_565.png": {
       "allowed-digests": [
         [
           "bitmap-64bitMD5", 
           14803637687851344622
         ]
       ], 
       "reviewed-by-human": true
@@ skipping 16669 matching lines @@
       "allowed-digests": [
         [
           "bitmap-64bitMD5", 
           11835374726311942978
         ]
       ], 
       "reviewed-by-human": true
     }
   }
 }