Update ps command in taskkill to also work on linux

R=kustermann@google.com

Review URL: https://codereview.chromium.org//23946003

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@27101 260f80e4-7a28-3924-810f-c04153c831b5

tools/task_kill.py

@@ -50,7 +50,7 @@ def GetOptions():
 def GetPidsPosix(process_name):
   # This is to have only one posix command, on linux we could just do:
   # pidof process_name
-  cmd = 'ps -e -o pid=,comm='
+  cmd = 'ps -e -o pid= -o comm='
   # Sample output:
   # 1 /sbin/launchd
   # 80943 /Applications/Safari.app/Contents/MacOS/Safari