[Refactor] Consolidate the logic for whether a widget can be activated.

ash/wm/dock/docked_window_layout_manager.cc

Index: ash/wm/dock/docked_window_layout_manager.cc
diff --git a/ash/wm/dock/docked_window_layout_manager.cc b/ash/wm/dock/docked_window_layout_manager.cc
index ab738eab79503d271274c304bef8d033d8ebb6c9..4391a7b6c8ccfcf150e025437232f71a08a01927 100644
--- a/ash/wm/dock/docked_window_layout_manager.cc
+++ b/ash/wm/dock/docked_window_layout_manager.cc
@@ -138,7 +138,6 @@ class DockedBackgroundWidget : public views::Widget,
     views::Widget::InitParams params;
     params.type = views::Widget::InitParams::TYPE_POPUP;
     params.opacity = views::Widget::InitParams::TRANSLUCENT_WINDOW;
-    params.can_activate = false;
     params.keep_on_top = false;
     params.ownership = views::Widget::InitParams::WIDGET_OWNS_NATIVE_WIDGET;
     params.parent = parent;