Set focusibility correctly when initializing a window in mus+ash.

services/ui/public/interfaces/window_manager.mojom

Index: services/ui/public/interfaces/window_manager.mojom
diff --git a/services/ui/public/interfaces/window_manager.mojom b/services/ui/public/interfaces/window_manager.mojom
index 9bc51f3eadc72b21714701fc41d972fd39ae6422..9e7f262af299727e78bef0bedb983f715ee42e10 100644
--- a/services/ui/public/interfaces/window_manager.mojom
+++ b/services/ui/public/interfaces/window_manager.mojom
@@ -35,6 +35,9 @@ interface WindowManager {
 
   // Properties used only during creation time. --------------------------------
 
+  // Whether the window should be initially focusable or not. Type: bool.
+  const string kFocusable_InitProperty = "init:focusable";
+
   // Initial bounds to create the window at. If empty the WindowManager decides
   // the initial bounds. Type: gfx::Rect.
   const string kBounds_InitProperty = "init:bounds";