Move ComputeDirectorySize to the base namespace.

BUG=
TBR=tfarina

Review URL: https://chromiumcodereview.appspot.com/16950027

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@208091 0039d316-1c4b-4281-b951-d872f2087c98

• base/file_util.cc[diff]
• base/file_util.h[diff]
• base/file_util_unittest.cc[diff]
• base/file_util_win.cc[diff]
• chrome/browser/chromeos/contacts/contact_database.cc[diff]
• chrome/browser/diagnostics/recon_diagnostics.cc[diff]
• content/browser/indexed_db/indexed_db_context_impl.cc[diff]
• webkit/browser/fileapi/sandbox_file_system_test_helper.cc[diff]