Skip absurdly slow PDF tests on Valgrind bot.

Our Valgrind-with-keepalive CPU bot is still running its first run as I write
this.  It's been going ~48 hours.  'pdf gm fontmgr_iter' finished after ~19
hours.  'pdf image PANO_20121023_214540.jpg' still seems to be running.

After this, the next slowest will be '565 gm fontmgr_iter' at about 37 minutes.

TBR=borenet@google.com

BUG=skia:

Review URL: https://codereview.chromium.org/1003423002
diff --git a/tools/dm_flags.py b/tools/dm_flags.py
index d00f74c..9e19e34 100755
--- a/tools/dm_flags.py
+++ b/tools/dm_flags.py
@@ -58,9 +58,12 @@
     blacklist.extend('gpu skp _ gpu image _ gpu subset _'.split(' '))
     blacklist.extend('msaa skp _ msaa image _ gpu subset _'.split(' '))
 
-  # PDF + .webp -> jumps depending on uninitialized memory.  skia:3505
   if 'Valgrind' in bot:
+    # PDF + .webp -> jumps depending on uninitialized memory.  skia:3505
     blacklist.extend('pdf _ .webp'.split(' '))
+    # These both take 18+ hours to run.
+    blacklist.extend('pdf gm fontmgr_iter'.split(' '))
+    blacklist.extend('pdf _ PANO_20121023_214540.jpg'.split(' '))
     if 'Valgrind_GPU' in bot:
       args.append('--nocpu')
     elif 'Valgrind_CPU' in bot: