Gate console.log output in Google Now

To reduce the chattiness of Google Now, localStorage.debug_mode for Google Now
and showConsoleLogOutput for unit tests will control when console.log actually
outputs to the console.

BUG=338239
TEST=By default, there will be no console.log output. When
localStorage.debug_mode is true in Google Now or showConsoleLogOutput is set
to true in unit tests, console.log output will occur.

Review URL: https://codereview.chromium.org/145353010

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247606 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 247606