Mark blurs-gpu test as known-to-fail on Nexus4

expectations/gm/Test-Android-Nexus4-Adreno320-Arm7-Debug/expected-results.json

 {
   "actual-results": {
     "failed": null, 
     "failure-ignored": null, 
     "no-comparison": null, 
     "succeeded": null
   }, 
   "expected-results": {
     "3x3bitmaprect_565.png": {
       "allowed-digests": [
@@ skipping 1690 matching lines @@
       ], 
       "reviewed-by-human": true
     }, 
     "blurs_gpu.png": {
       "allowed-digests": [
         [
           "bitmap-64bitMD5", 
           3716091659075403920
         ]
       ], 
+      "bugs": [
+        1791
+      ], 
+      "ignore-failure": true, 
       "reviewed-by-human": true
     }, 
     "canvas-layer-state_565.png": {
       "allowed-digests": [
         [
           "bitmap-64bitMD5", 
           9377267151286982251
         ]
       ], 
       "reviewed-by-human": true
@@ skipping 5585 matching lines @@
     "xfermodes_gpu.png": {
       "allowed-digests": [
         [
           "bitmap-64bitMD5", 
           1506273902709442856
         ]
       ], 
       "reviewed-by-human": true
     }
   }
-}
+}