Update edgeBackGestureHandler for Taskbar on init/destroy()

* TaskbarDelegate wasn't calling
mEdgeBackGestureHandler.onNavBarDetatched() when going from
large screen to phone screen
* Also cache taskbar visibility to prevent multiple instances
of the same listener from being added

Bug: 197058461
Test: Went from tablet to phone, used back,
saw Launcher#onBackPressed() only got called once

Change-Id: I63b742b047cbfac1421c5a0e8422e9e341c62627

packages/SystemUI/src/com/android/systemui/navigationbar/TaskbarDelegate.java

@@ -71,6 +71,7 @@ public class TaskbarDelegate implements CommandQueue.Callbacks,
     private int mDisabledFlags;
     private @WindowVisibleState int mTaskBarWindowState = WINDOW_STATE_SHOWING;
     private @Behavior int mBehavior;
+    private boolean mTaskbarVisible = false;
 
     @Inject
     public TaskbarDelegate(Context context) {
@@ -96,6 +97,8 @@ public class TaskbarDelegate implements CommandQueue.Callbacks,
         mOverviewProxyService.removeCallback(this);
         mNavigationModeController.removeListener(this);
         mNavigationBarA11yHelper.removeA11yEventListener(mNavA11yEventListener);
+        mEdgeBackGestureHandler.onNavBarDetached();
+        mTaskbarVisible = false;
     }
 
     public void init(int displayId) {
@@ -104,6 +107,8 @@ public class TaskbarDelegate implements CommandQueue.Callbacks,
         mOverviewProxyService.addCallback(this);
         mNavigationModeController.addListener(this);
         mNavigationBarA11yHelper.registerA11yEventListener(mNavA11yEventListener);
+        mEdgeBackGestureHandler.onNavBarAttached();
+        mTaskbarVisible = true;
         // Set initial state for any listeners
         updateSysuiFlags();
     }
@@ -180,6 +185,10 @@ public class TaskbarDelegate implements CommandQueue.Callbacks,
 
     @Override
     public void onTaskbarStatusUpdated(boolean visible, boolean stashed) {
+        if (mTaskbarVisible == visible) {
+            return;
+        }
+        mTaskbarVisible = visible;
         if (visible) {
             mEdgeBackGestureHandler.onNavBarAttached();
         } else {