Some updates to the pages framework on master had made the HeaderView a

singleton object. This caused conflicts when running the tests, since

a HeaderView is instantiated by the test page, and then each of the

individual pages would create additional ones when they were being

tested.
The tests for the individual pages are pretty isolated, and access the

HeaderView through their stored attributes instead of as a singleton.

It's therefore safe to have multiple ones when we're in the context of

the test runner. This change adds spies in the right place to suppress

the warnings.

Ran the JS test suite and saw that a bunch of warnings about duplicate

singleton objects no longer showed up.