Use hasattr to test CTracer support.
Use hasattr to test CTracer support.

Otherwise the program dies with:
AttributeError: 'module' object has no attribute 'CTracer'

and never prints the subsequent help message.

R=iannucci@chromium.org

Review URL: https://codereview.chromium.org/180383005

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@254882 0039d316-1c4b-4281-b951-d872f2087c98

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