Fix the UrlToFilenameEncoder to be more cross platform. FilePath::StringType on linux is a std::string, while on Windows it is a std::wstring.  The old implementation assumed wstrings.  Rework the class to deal entirely with narrow strings (since wide-strings are not relevant for this utility).
Fix the UrlToFilenameEncoder to be more cross platform.
FilePath::StringType on linux is a std::string, while on Windows it is a
std::wstring.  The old implementation assumed wstrings.  Rework the class
to deal entirely with narrow strings (since wide-strings are not relevant
for this utility).

Note: This file is only used in some tools.

BUG=none
TEST=none


Review URL: http://codereview.chromium.org/261001

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@28224 0039d316-1c4b-4281-b951-d872f2087c98

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