Log when app move to foreground or background.

Together with screen state change, we will have appusage info.

Test: manually test on device
Change-Id: Ie9cfe0376cf0d6339be5e8e96f7b360c3f0771d6

cmds/statsd/src/stats_events.proto

@@ -71,6 +71,7 @@ message StatsEvent {
         PhoneSignalStrengthChanged phone_signal_strength_changed = 40;
         SettingChanged setting_changed = 41;
         KernelWakelockPulled kernel_wakelock_pulled = 42;
+        ActivityForegroundStateChanged activity_foreground_state_changed = 43;
         // TODO: Reorder the numbering so that the most frequent occur events occur in the first 15.
     }
 }
@@ -693,3 +694,20 @@ message KernelWakelockPulled {
     optional int64 total_time = 3;
     optional string name = 4;
 }
+
+/*
+ * Logs activity going to foreground or background
+ *
+ * Logged from:
+  *   frameworks/base/services/core/java/com/android/server/am/ActivityRecord.java
+ */
+message ActivityForegroundStateChanged {
+    enum Activity {
+        MOVE_TO_BACKGROUND = 0;
+        MOVE_TO_FOREGROUND = 1;
+    }
+    optional int32 uid = 1;
+    optional string pkg_name = 2;
+    optional string class_name = 3;
+    optional Activity activity = 4;
+}

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

@@ -4043,10 +4043,14 @@ public class ActivityManagerService extends IActivityManager.Stub
         if (DEBUG_SWITCH) Slog.d(TAG_SWITCH,
                 "updateUsageStats: comp=" + component + "res=" + resumed);
         final BatteryStatsImpl stats = mBatteryStatsService.getActiveStatistics();
+        StatsLog.write(StatsLog.ACTIVITY_FOREGROUND_STATE_CHANGED,
+            component.userId, component.realActivity.getPackageName(),
+            component.realActivity.getShortClassName(), resumed ? 1 : 0);
         if (resumed) {
             if (mUsageStatsService != null) {
                 mUsageStatsService.reportEvent(component.realActivity, component.userId,
                         UsageEvents.Event.MOVE_TO_FOREGROUND);
+
             }
             synchronized (stats) {
                 stats.noteActivityResumedLocked(component.app.uid);