Add support for pinning platform apps

ash/launcher/launcher_view.cc

Index: ash/launcher/launcher_view.cc
diff --git a/ash/launcher/launcher_view.cc b/ash/launcher/launcher_view.cc
index c780039dbab8bfad28472aa76ae12af3b99f586c..132e3b3dd2c9b7e97c02016ec3d67b3258800870 100644
--- a/ash/launcher/launcher_view.cc
+++ b/ash/launcher/launcher_view.cc
@@ -627,11 +627,13 @@ bool LauncherView::SameDragType(LauncherItemType typea,
   switch (typea) {
     case TYPE_TABBED:
     case TYPE_APP_PANEL:
-      return (typeb == TYPE_TABBED || typeb == TYPE_APP_PANEL);
+    case TYPE_PLATFORM_APP:
+      return (typeb == TYPE_TABBED ||
+          typeb == TYPE_APP_PANEL ||
+          typeb == TYPE_PLATFORM_APP);
     case TYPE_APP_SHORTCUT:
     case TYPE_APP_LIST:
     case TYPE_BROWSER_SHORTCUT:
-    case TYPE_PLATFORM_APP:
       return typeb == typea;
   }
   NOTREACHED();