A service that responds to changes in one or more sources. These sources can
be plugged into the service. Sources represent a common event framework for
services.
Adds a source provider to this service. A source provider will notify the
service when the source it provides changes. An example of a source might
be an active editor or the current selection. This amounts to a pluggable
state tracker for the service.
Parameters: provider - The provider to add; must not be null.
Removes a source provider from this service. Most of the time, this
method call is not required as source providers typically share the same
life span as the workbench itself.
Parameters: provider - The provider to remove; must not be null.