Creating default implementation for state lisnter method

> The transition start is used rarely

Change-Id: I0d33f0f6372eb4ef89bfbb66968612693b7c6033

src/com/android/launcher3/Launcher.java

@@ -434,9 +434,6 @@ public class Launcher extends BaseDraggingActivity implements LauncherExterns,
         mRotationHelper.initialize();
 
         mStateManager.addStateListener(new LauncherStateManager.StateListener() {
-            @Override
-            public void onStateTransitionStart(LauncherState toState) {
-            }
 
             @Override
             public void onStateTransitionComplete(LauncherState finalState) {

src/com/android/launcher3/LauncherStateManager.java

@@ -600,7 +600,8 @@ public class LauncherStateManager {
 
     public interface StateListener {
 
-        void onStateTransitionStart(LauncherState toState);
-        void onStateTransitionComplete(LauncherState finalState);
+        default void onStateTransitionStart(LauncherState toState) { }
+
+        default void onStateTransitionComplete(LauncherState finalState) { }
     }
 }

src/com/android/launcher3/dragndrop/DragView.java

@@ -175,9 +175,6 @@ public class DragView extends View implements LauncherStateManager.StateListener
         mLauncher.getStateManager().removeStateListener(this);
     }
 
-    @Override
-    public void onStateTransitionStart(LauncherState toState) { }
-
     @Override
     public void onStateTransitionComplete(LauncherState finalState) {
         setVisibility((finalState == LauncherState.NORMAL

src/com/android/launcher3/views/ScrimView.java

@@ -117,9 +117,6 @@ public class ScrimView<T extends Launcher> extends View implements Insettable, O
     protected final int mEndScrim;
 
     private final StateListener mAccessibilityLauncherStateListener = new StateListener() {
-        @Override
-        public void onStateTransitionStart(LauncherState toState) {}
-
         @Override
         public void onStateTransitionComplete(LauncherState finalState) {
             setImportantForAccessibility(finalState == ALL_APPS

src/com/android/launcher3/views/WorkEduView.java

@@ -188,11 +188,6 @@ public class WorkEduView extends AbstractSlideInView implements Insettable {
         }
 
         LauncherStateManager.StateListener listener = new LauncherStateManager.StateListener() {
-            @Override
-            public void onStateTransitionStart(LauncherState toState) {
-
-            }
-
             @Override
             public void onStateTransitionComplete(LauncherState finalState) {
                 if (finalState != LauncherState.ALL_APPS) return;