Add initial baselines for discard GM

expectations/gm/Test-Win8-ShuttleA-HD7770-x86-Debug/expected-results.json

 {
   "expected-results": {
     "3x3bitmaprect_565.png": {
       "allowed-digests": [
         [
           "bitmap-64bitMD5", 
           12831071530564277917
         ]
       ], 
       "bugs": [
@@ skipping 4824 matching lines @@
         [
           "bitmap-64bitMD5", 
           7819825549601859094
         ]
       ], 
       "bugs": [
         1935
       ], 
       "reviewed-by-human": false
     }, 
+    "discard_gpu.png": {
+      "allowed-digests": [
+        [
+          "bitmap-64bitMD5", 
+          11635187478196931850
+        ]
+      ], 
+      "reviewed-by-human": true
+    }, 
     "displacement_565.png": {
       "allowed-digests": [
         [
           "bitmap-64bitMD5", 
           9127724751254250264
         ]
       ], 
       "bugs": [
         1935
       ], 
@@ skipping 8105 matching lines @@
           14019814087375927425
         ]
       ], 
       "bugs": [
         1935
       ], 
       "reviewed-by-human": false
     }
   }
 }