Ignore failure of mixed_xfermodes_gpu on N4

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

 {
   "expected-results": {
     "3x3bitmaprect_565.png": {
       "allowed-digests": [
         [
           "bitmap-64bitMD5", 
           16998423976396106083
         ]
       ], 
       "bugs": [
@@ skipping 6898 matching lines @@
       ], 
       "bugs": [
         2146
       ], 
       "reviewed-by-human": false
     }, 
     "mixed_xfermodes_gpu.png": {
       "allowed-digests": [
         [
           "bitmap-64bitMD5", 
-          10531722056214126451
+          7758597652352633244
         ]
       ], 
       "bugs": [
-        2146
+        1596
       ], 
+      "ignore-failure": true, 
       "reviewed-by-human": true
     }, 
     "modecolorfilters_565.png": {
       "allowed-digests": [
         [
           "bitmap-64bitMD5", 
           2595933616904054518
         ]
       ], 
       "bugs": [
@@ skipping 2936 matching lines @@
           187105012410000322
         ]
       ], 
       "bugs": [
         2146
       ], 
       "reviewed-by-human": false
     }
   }
 }