Background tracing: Remove command_line from whitelist

BUG=770017
R=ssid
CC=erikchen

Change-Id: I65ad6e70fc5ee5461275b37f8e42b566ad2fb84a
Reviewed-on: https://chromium-review.googlesource.com/695904Reviewed-by: Siddhartha S <ssid@chromium.org>
Commit-Queue: oysteine <oysteine@chromium.org>
Cr-Commit-Position: refs/heads/master@{#505907}

chrome/common/trace_event_args_whitelist.cc

@@ -35,7 +35,6 @@ const WhitelistEntry kEventArgsWhitelist[] = {
 
 const char* kMetadataWhitelist[] = {
   "clock-domain",
-  "command_line",
   "config",
   "cpu-*",
   "field-trials",