Ignore failures in mixed_xfermodes_gpu GM test on Nexus 4

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 5814 matching lines @@
       "reviewed-by-human": false
     }, 
     "mixed_xfermodes_gpu.png": {
       "allowed-digests": [
         [
           "bitmap-64bitMD5", 
           13603092541584912268
         ]
       ], 
       "bugs": [
-        1578
+        1596
       ], 
+      "ignore-failure": true, 
       "reviewed-by-human": false
     }, 
     "modecolorfilters_565.png": {
       "allowed-digests": [
         [
           "bitmap-64bitMD5", 
           2595933616904054518
         ]
       ], 
       "bugs": [
@@ skipping 2275 matching lines @@
       "allowed-digests": [
         [
           "bitmap-64bitMD5", 
           9019242913965337895
         ]
       ], 
       "ignore-failure": false
     }
   }
 }