A class that manages the task of watching for and connecting to new
source pads by name. The inputs are an element, the name of the
source pad to watch for on that element, and the sink pad (on a
different element) to which the source pad should be linked when it
appears.
The "pad-added" signal of the element will be used to watch for new
pads, and if the "no-more-pads" signal is emitted by the element
before the requested pad has appeared ValueError is raised.
Definition at line 53 of file source.py.