Clean up back handler from prototracer

Bug: 160161606
Test: Switch darkmode serveral times and verify there aren't
      old refs in the heap dump
Change-Id: I1678d10e725f6bdcbc807064413b4bc549ef8ef2

packages/SystemUI/src/com/android/systemui/statusbar/phone/EdgeBackGestureHandler.java

@@ -231,7 +231,6 @@ public class EdgeBackGestureHandler extends CurrentUserTracker implements Displa
             }
         }
 
-        Dependency.get(ProtoTracer.class).add(this);
         mLongPressTimeout = Math.min(MAX_LONG_PRESS_TIMEOUT,
                 ViewConfiguration.getLongPressTimeout());
 
@@ -286,6 +285,7 @@ public class EdgeBackGestureHandler extends CurrentUserTracker implements Displa
      */
     public void onNavBarAttached() {
         mIsAttached = true;
+        Dependency.get(ProtoTracer.class).add(this);
         mOverviewProxyService.addCallback(mQuickSwitchListener);
         updateIsEnabled();
         startTracking();
@@ -296,6 +296,7 @@ public class EdgeBackGestureHandler extends CurrentUserTracker implements Displa
      */
     public void onNavBarDetached() {
         mIsAttached = false;
+        Dependency.get(ProtoTracer.class).remove(this);
         mOverviewProxyService.removeCallback(mQuickSwitchListener);
         updateIsEnabled();
         stopTracking();