Let BaseChromiumApplication manage the tracing controller

- Reduce duplicated code;
- Allow tracing during the whole life cycle of the application (TODO:
  support tracing before the native library is loaded);
- Avoid conflict between multiple tracing controllers.

Review URL: https://codereview.chromium.org/26740005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228839 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228839