Be more strict about content types for message array

Now with fewer class cast exceptions

Test: ConversationNotification
Test: NotificationManagerServiceTest
Bug: 433746973
Flag: EXEMPT BUGFIX
(cherry picked from commit 71d4afae00c7d6d9238f8ec82303e1e13da50fbb)
Cherrypick-From: https://googleplex-android-review.googlesource.com/q/commit:f64c1e377842d9a8df814bcbad831bd4ce01583d
Merged-In: I3022e010de95f14dcd0d09d123684ee265101e0a
Change-Id: I3022e010de95f14dcd0d09d123684ee265101e0a
2 files changed