Fix security issue

Settings#CredentialStorage could be overlaid to
trick user into clearing all credentials.

Disallow non-system overlay on activity.

Test: Trigger the debug apk again, and no overlay
Bug: 176753731
Change-Id: I657de039d667f5aee0941336e9361ae04f056c33
Merged-In: I657de039d667f5aee0941336e9361ae04f056c33
1 file changed