According to our style guide on Copyable and Movable Types,
copy/move operators should be disabled in the public: section, not
in the private: section. If disabled with a macro such as
DISALLOW_COPY_AND_ASSIGN, it should be at the end of the private: section,
and should be the last thing in the class.

BUG=

Review-Url: https://codereview.chromium.org/2271043003
Cr-Commit-Position: refs/heads/master@{#38878}