Refactor in PositionTesterContextMenuListener.

The asserts were removed from that class and replaced by a status String object.

This allows ExpandableListTester to do the asserts instead.
These tests passed on a sapphire and passion devices as well as in the emulator.
The asserts in the main thread are expected to make these tests pass during the
continuous build too.

This is 7fbddb1d cherrypicked to froyo.

http://b/issue?id=2525846