Switching all wstrings in courgette_tool to FilePaths.
Switching all wstrings in courgette_tool to FilePaths.

Presubmit checks now consider the presence of wstring to be an error, so
switching all wstrings in courgette_tool to FilePath's as evanm had
already called out in a TODO.

BUG=chromiumos:22693


Review URL: http://codereview.chromium.org/8498032

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@110611 0039d316-1c4b-4281-b951-d872f2087c98

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