Better ContentProvider error messages.

Help guide developers towards ACTION_OPEN_DOCUMENT and related
APIs when a Uri is backed by a DocumentProvider.

Also help developer understand that we expected a valid
ContentProvider for Uri notifications.

Test: builds, boots
Bug: 32642790, 36075317
Change-Id: I8e0e3cb25b183c4a9a094a53018822a4212bdaf9
2 files changed