Blacklisting imagefilterscropexpand on s4 since it often causes the bot to hang and crash.

BUG=skia:4079

Review URL: https://codereview.chromium.org/1373763005

tools/dm_flags.json

@@ -402,6 +402,7 @@
     "~tabl_mozilla_0", 
     "~desk_yahoonews_0", 
     "~imagefiltersclipped", 
+    "~imagefilterscropexpand", 
     "~scaled_tilemodes_npot", 
     "~bleed_image", 
     "~ReadPixels"

tools/dm_flags.py

@@ -171,6 +171,7 @@ def get_args(bot):
 
   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