Add initial baselines for discard GM

expectations/gm/Test-Win7-ShuttleA-HD2000-x86-Release/expected-results.json

 {
   "expected-results": {
     "3x3bitmaprect_565.png": {
       "allowed-digests": [
         [
           "bitmap-64bitMD5", 
           9785004568147979273
         ]
       ], 
       "bugs": [
@@ skipping 4575 matching lines @@
         [
           "bitmap-64bitMD5", 
           5221011637067649849
         ]
       ], 
       "bugs": [
         2146
       ], 
       "reviewed-by-human": false
     }, 
+    "discard_gpu.png": {
+      "allowed-digests": [
+        [
+          "bitmap-64bitMD5", 
+          17913590323992569598
+        ]
+      ], 
+      "reviewed-by-human": true
+    }, 
     "displacement_565.png": {
       "allowed-digests": [
         [
           "bitmap-64bitMD5", 
           16066407771974797763
         ]
       ], 
       "bugs": [
         2146
       ], 
@@ skipping 8362 matching lines @@
           15843716056234692659
         ]
       ], 
       "bugs": [
         2146
       ], 
       "reviewed-by-human": false
     }
   }
 }