Log the event for swiping up to dismiss a task in Overview.

Test: manual
Bug: 137777105

Demo logging for dismissing a task:
  data {
    elapsed_timestamp_nanos: 70772067228810
    atom {
      launcher_event {
        action: DISMISS_TASK
        src_state: OVERVIEW
        dst_state: BACKGROUND
        is_swipe_up_enabled: true
      }
    }
  }

Change-Id: I5569b80e2e1f35661bc5e9e343c6c298791a1ec1

src/com/android/launcher3/logging/StatsLogManager.java

@@ -40,5 +40,6 @@ public class StatsLogManager implements ResourceBasedOverride {
 
     public void logAppLaunch(View v, Intent intent) { }
     public void logTaskLaunch(View v, ComponentKey key) { }
+    public void logTaskDismiss(View v, ComponentKey key) { }
     public void verify() {}     // TODO: should move into robo tests
 }