Track double taps to launch the previous task.

Change-Id: Icd792ed4f508f8a8540a5cd2d12c3bdfd5827410
diff --git a/packages/SystemUI/src/com/android/systemui/recents/views/TaskStackView.java b/packages/SystemUI/src/com/android/systemui/recents/views/TaskStackView.java
index afa5188..e1a81c8 100644
--- a/packages/SystemUI/src/com/android/systemui/recents/views/TaskStackView.java
+++ b/packages/SystemUI/src/com/android/systemui/recents/views/TaskStackView.java
@@ -1573,6 +1573,9 @@
             Task launchTask = mStack.getStackTasks().get(launchTaskIndex);
             EventBus.getDefault().send(new LaunchTaskEvent(getChildViewForTask(launchTask),
                     launchTask, null, INVALID_STACK_ID, false /* screenPinningRequested */));
+
+            MetricsLogger.action(getContext(), MetricsEvent.OVERVIEW_LAUNCH_PREVIOUS_TASK,
+                    launchTask.key.getComponent().toString());
         }
     }
 
diff --git a/proto/src/metrics_constants.proto b/proto/src/metrics_constants.proto
index 49972d6..568edab 100644
--- a/proto/src/metrics_constants.proto
+++ b/proto/src/metrics_constants.proto
@@ -447,5 +447,8 @@
 
     // Logs the action the user takes when an app ANR'd.
     ACTION_APP_ANR = 317;
+
+    // Logged when a user double taps the overview button to launch the previous task
+    OVERVIEW_LAUNCH_PREVIOUS_TASK = 318;
   }
 }