Change focused window when scrolling over appIcon

appIcons.js

@@ -197,6 +197,8 @@ var taskbarAppIcon = Utils.defineClass({
                                                 Lang.bind(this, this._updateWindowTitle));
         }
         
+        this._scrollEventId = this.actor.connect('scroll-event', this._onMouseScroll.bind(this));
+
         this._overviewWindowDragEndId = Main.overview.connect('window-drag-end',
                                                 Lang.bind(this, this._onOverviewWindowDragEnd));
 
@@ -296,6 +298,10 @@ var taskbarAppIcon = Utils.defineClass({
             this.actor.disconnect(this._hoverChangeId);
         }
 
+        if (this._scrollEventId) {
+            this.actor.disconnect(this._scrollEventId);
+        }
+
         for (let i = 0; i < this._dtpSettingsSignalIds.length; ++i) {
             this._dtpSettings.disconnect(this._dtpSettingsSignalIds[i]);
         }
@@ -334,6 +340,35 @@ var taskbarAppIcon = Utils.defineClass({
         });
     },
 
+    _onMouseScroll: function(actor, event) {
+        if (!this.window && !this._nWindows) {
+            return;
+        }
+
+        let direction = Utils.getMouseScrollDirection(event);
+
+        if (direction) {
+            let windows = this.getAppIconInterestingWindows();
+            
+            windows.sort(Taskbar.sortWindowsCompareFunction);
+
+            let windowIndex = windows.indexOf(global.display.focus_window);
+            let nextWindowIndex = windowIndex < 0 ?
+                                  this.window ? windows.indexOf(this.window) : 0 : 
+                                  windowIndex + (direction == 'up' ? 1 : -1);
+
+            if (nextWindowIndex == windows.length) {
+                nextWindowIndex = 0;
+            } else if (nextWindowIndex < 0) {
+                nextWindowIndex = windows.length - 1;
+            }
+
+            if (windowIndex != nextWindowIndex) {
+                Main.activateWindow(windows[nextWindowIndex]);
+            }
+        }
+    },
+    
     _showDots: function() {
         // Just update style if dots already exist
         if (this._focusedDots && this._unfocusedDots) {

panel.js

@@ -743,18 +743,7 @@ var dtpPanelWrapper = Utils.defineClass({
     },
 
     _onPanelMouseScroll: function(actor, event) {
-        let direction = 0;
-
-        switch (event.get_scroll_direction()) {
-            case Clutter.ScrollDirection.UP:
-            case Clutter.ScrollDirection.LEFT:
-                direction = 'up';
-                break;
-            case Clutter.ScrollDirection.DOWN:
-            case Clutter.ScrollDirection.RIGHT:
-                direction = 'down';
-                break;
-        }
+        let direction = Utils.getMouseScrollDirection(event);
 
         if (direction) {
             Main.wm._showWorkspaceSwitcher(global.display, 0, { get_name: () => 'switch---' + direction });

utils.js

@@ -380,6 +380,23 @@ var getrgbaColor = function(color, alpha, offset) {
     return 'rgba(' + rgb.red + ',' + rgb.green + ',' + rgb.blue + ',' + (Math.floor(alpha * 100) * 0.01) + '); ' ;
 };
 
+var getMouseScrollDirection = function(event) {
+    let direction;
+
+    switch (event.get_scroll_direction()) {
+        case Clutter.ScrollDirection.UP:
+        case Clutter.ScrollDirection.LEFT:
+            direction = 'up';
+            break;
+        case Clutter.ScrollDirection.DOWN:
+        case Clutter.ScrollDirection.RIGHT:
+            direction = 'down';
+            break;
+    }
+
+    return direction;
+};
+
 /*
  * This is a copy of the same function in utils.js, but also adjust horizontal scrolling
  * and perform few further cheks on the current value to avoid changing the values when