Generate app and device screen-on time data and return back to UI for

rendering.

Test: make RunSettingsRoboTests + manually
Bug: 260964903
Change-Id: I2fd69b4686cc2e1413ad0eb43c07b6164e411411

src/com/android/settings/fuelgauge/protos/app_usage_event.proto

@@ -40,3 +40,16 @@ message AppUsagePeriod {
   // End of the usage period.
   optional int64 end_time = 2;
 }
+
+enum AppUsageEndPointType {
+  START = 1;
+  END = 2;
+}
+
+// The endpoint (the beginning or the end) of an AppUsagePeriod.
+message AppUsageEndPoint {
+  // Type of the end point.
+  optional AppUsageEndPointType type = 1;
+  // Timestamp of the end point.
+  optional int64 timestamp = 2;
+}