history: Make QueryNodeList more readable.
history: Make QueryNodeList more readable.

- Group all the overridden methods.
- Add OVERRIDE to them.
- Move the implementation out of the class declaration.
- Fix the order to match with our style.
- Use STLDeleteElements.
- Add DISALLOW_COPY_AND_ASSIGN.

BUG=68682
TEST=None

R=sky@chromium.org

Review URL: http://codereview.chromium.org/6904087

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@83453 0039d316-1c4b-4281-b951-d872f2087c98

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