Skip downloading symbols if they're not available
Skip downloading symbols if they're not available

Remove the warning return code because buildbot will halt for any unsuccessful code for this step.

NOTRY=true

Review URL: https://chromiumcodereview.appspot.com/12041065

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@178453 0039d316-1c4b-4281-b951-d872f2087c98

eunchong/build,eunchong/build,eunchong/build,eunchong/build