Add initial baselines for discard GM

expectations/gm/Test-Mac10.8-MacMini4.1-GeForce320M-x86_64-Release/expected-results.json

 {
   "actual-results": {
     "failed": null, 
     "failure-ignored": null, 
     "no-comparison": null, 
     "succeeded": null
   }, 
   "expected-results": {
     "3x3bitmaprect_565.png": {
       "allowed-digests": [
@@ skipping 5445 matching lines @@
         [
           "bitmap-64bitMD5", 
           4664344770323231961
         ]
       ], 
       "bugs": [
         1578
       ], 
       "reviewed-by-human": false
     }, 
+    "discard_gpu.png": {
+      "allowed-digests": [
+        [
+          "bitmap-64bitMD5", 
+          11635187478196931850
+        ]
+      ], 
+      "reviewed-by-human": true
+    }, 
     "displacement_565.png": {
       "allowed-digests": [
         [
           "bitmap-64bitMD5", 
           7360996518918447134
         ]
       ], 
       "bugs": [
         1578
       ], 
@@ skipping 9396 matching lines @@
           7829854837061118142
         ]
       ], 
       "bugs": [
         1578
       ], 
       "reviewed-by-human": false
     }
   }
 }