Adjust behavior of search results to match app well

Currently, activating a search result always opens a new window. Change
this behavior, so that if an application has open windows, the most
recently used one is activated instead.

Also change the implementation of dnd of search results to allow providers
to treat results activated via dnd differently.

https://bugzilla.gnome.org/show_bug.cgi?id=610027

js/ui/appDisplay.js

@@ -236,6 +236,16 @@ BaseAppSearchProvider.prototype = {
     },
 
     activateResult: function(id) {
+        let app = this._appSys.get_app(id);
+        let windows = app.get_windows();
+
+        if (windows.length > 0)
+            Main.overview.activateWindow(windows[0], global.get_current_time());
+        else
+            app.launch();
+    },
+
+    dragActivateResult: function(id) {
         let app = this._appSys.get_app(id);
         app.launch();
     }

js/ui/dash.js

@@ -390,7 +390,10 @@ SearchResult.prototype = {
     },
 
     shellWorkspaceLaunch: function() {
-        this.provider.activateResult(this.metaInfo.id);
+        if (this.provider.dragActivateResult)
+            this.provider.dragActivateResult(this.metaInfo.id);
+        else
+            this.provider.activateResult(this.metaInfo.id);
     }
 }