Move event-firing into Storage interface instead of action at a distance

[domenic]

Currently the firing of storage events is done at a distance, via these paragraphs:

When the setItem(), removeItem(), and clear() methods are called on a Storage object x that is associated with a session storage area, if the methods did not throw an exception or "do nothing" as defined above, then for every Document object whose Window object's sessionStorage attribute's Storage object is associated with the same storage area, other than x, send a storage notification.

When the setItem(), removeItem(), and clear() methods are called on a Storage object x that is associated with a local storage area, if the methods did not throw an exception or "do nothing" as defined above, then for every Document object whose Window object's localStorage attribute's Storage object is associated with the same storage area, other than x, send a storage notification.

These should move into the algorithms for setItem/removeItem/clear, and use actual if statements, and so on.

Formalizing this probably requires some kind of mapping back from storage areas to Storage instances.