CPP: Fix compilation error on Clang.
CPP: Fix compilation error on Clang.

This fixes a compilation error on Clang due to conflicting declarations (struct
vs class) in multiple header files.

BUG=http://crbug.com/236272
R=jia.shao.peng@gmail.com

Review URL: https://codereview.appspot.com/9259043

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