[EME] Bug 18531 - rename addKey method

https://www.w3.org/Bugs/Public/show_bug.cgi?id=18531


The addKey method can be used for more than just providing a key. Specifically
it can be used for
- providing a key
- providing a license
- updating a license or other CDM session state

As a result the addKey name is confusing.

In general, the purpose of this method is to provide a message to the CDM that
updates the session state in some CDM-specific way. With the object-oriented
model, sessions are explicitly represented by session objects and addKey is a
method on that object.

With that context we could rename the method to something simple.

Proposals so far:

- update() (as in update the session state)

- addData() (as in provide some information to the session)

Comments, preferences, other suggestions ?

…Mark