Add SCOPED_TRACEs to ICUStringConversionsTest to help debug http://bugs.gentoo.org/show_bug.cgi?id=350347
Add SCOPED_TRACEs to ICUStringConversionsTest
to help debug http://bugs.gentoo.org/show_bug.cgi?id=350347

They are also useful in general, so I don't plan to remove them later.

BUG=none
TEST=none
Review URL: http://codereview.chromium.org/5982003

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@70430 0039d316-1c4b-4281-b951-d872f2087c98

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