Make some ChooserActivity inner classes static.

This helps clarify the (lack of) dependencies between these
classes, and suggests that some of them might make good
candidates for removal from the (large) main source file.

In most cases, the classes already had no dependencies and
were ready to switch to static. In one case I had to modify
a class to make its single dependency more explicit.

The few remaining non-static inner classes have more
intricate dependencies on ChooserActivity, and should be
considered in a separate CL.

Test: build/presubmits (no behavior change)
Change-Id: Ic075f1bdd267cc16f6b7b297c7425873eb9bae55