Re-enable WritePixels test for iOS

tools/dm_flags.py

 #
 # Copyright 2015 Google Inc.
 #
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 #
 
 #!/usr/bin/env python
 
 usage = '''
@@ skipping 169 matching lines @@
 
   if 'GalaxyS3' in bot:  # skia:1699
     match.append('~WritePixels')
   
   if 'AndroidOne' in bot:  # skia:4711
     match.append('~WritePixels')
 
   if 'NexusPlayer' in bot:
     match.append('~ResourceCache')
 
-  if 'iOS' in bot:
-    match.append('~WritePixels')
-
   if 'GalaxyS4' in bot:  # skia:4079
     match.append('~imagefiltersclipped')
     match.append('~imagefilterscropexpand')
     match.append('~scaled_tilemodes_npot')
     match.append('~bleed_image')  # skia:4367
     match.append('~ReadPixels')  # skia:4368
 
   if match:
     args.append('--match')
     args.extend(match)
@@ skipping 42 matching lines @@
   if len(sys.argv) == 2 and sys.argv[1] == 'test':
     self_test()
     sys.exit(0)
 
   if len(sys.argv) != 3:
     print usage
     sys.exit(1)
 
   with open(sys.argv[1], 'w') as out:
     json.dump(get_args(sys.argv[2]), out)