Add event logging for UserState transitions.

Event log sticks around longer, and will help debug timing issues.

Test: builds and boots
Bug: 32719353
Change-Id: Ie19f76a341c58a8efee0eb1edbf183c22e9c5270

services/core/java/com/android/server/am/EventLogTags.logtags

@@ -112,3 +112,5 @@ option java_package com.android.server.am
 # Report changing memory conditions (Values are ProcessStats.ADJ_MEM_FACTOR* constants)
 30050 am_mem_factor (Current|1|5),(Previous|1|5)
 
+# UserState has changed
+30051 am_user_state_changed (id|1|5),(state|1|5)

services/core/java/com/android/server/am/UserState.java

@@ -70,6 +70,7 @@ public final class UserState {
     public boolean setState(int oldState, int newState) {
         if (state == oldState) {
             setState(newState);
+            EventLogTags.writeAmUserStateChanged(mHandle.getIdentifier(), newState);
             return true;
         } else {
             Slog.w(TAG, "Expected user " + mHandle.getIdentifier() + " in state "