Add a using declaration so that the overrides don't hide some of the base class methods.
Add a using declaration so that the overrides don't hide some of the
base class methods.

This was caught by GCC's -Woverloaded-virtual, not sure why it wasn't
caught by Clang's. =/

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@272460 91177308-0d34-0410-b5e6-96231b3b80d8

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