Bug 449546 - [responsiveness] No error logged when UI froze during
opening type hierarchy on java.lang.Object on Mac

This change adds a reference to the original event to PreEvent and
PostEvent. UI Responsiveness Monitoring will use this reference to do
additional filtering.

Change-Id: Ie3d27a9f4a0859aceefe719551445969d90c32e3
Signed-off-by: Sergey Prigogin <eclipse.sprigogin@gmail.com>