Fix a gcc warning seen in Chromium OS build.
Fix a gcc warning seen in Chromium OS build.

Please note that gcc's warn_unused_result check is enforced on the build environment. Anyway, I believe it's good to check the return value in this case.

BUG=none
TEST=ran emerge-x86-generic ibus.

Review URL: http://codereview.appspot.com/3904044

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