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:01326d2f6a1b80825b85992b35ce6d43af21a5c7
Merged-In: I3022e010de95f14dcd0d09d123684ee265101e0a
Change-Id: I3022e010de95f14dcd0d09d123684ee265101e0a
2 files changed