Enables WebCache columns on OS X's task manager.
Enables WebCache columns on OS X's task manager.

TEST=Enabled the Task Manager context menu, opened, enabled columns and observed values that look reasonable.
BUG=16221

Review URL: http://codereview.chromium.org/243006

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@27270 0039d316-1c4b-4281-b951-d872f2087c98

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