mash: Fix shelf window property use in Chrome.

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 9a2545ff408652d91933d7a84ce1b3b4e3893549..1a090b7d351b2203cb1f2e67864f2b8117b68b32 100644
--- a/services/ui/public/interfaces/window_manager.mojom
+++ b/services/ui/public/interfaces/window_manager.mojom
@@ -53,6 +53,8 @@ interface WindowManager {
   const string kShadowStyle_Property = "prop:shadow-style";
   // The image resource ID to be used as the shelf item's icon. Type: int
   const string kShelfIconResourceId_Property = "prop:shelf-icon-resource-id";
+  // The ID of the shelf item corresponding to this window. Type: int
+  const string kShelfId_Property = "prop:shelf-id";
   // The type of item to be shown on the shelf for this window. Type: int
   // A few ash::ShelfItemType values are supported; TYPE_UNKNOWN means no item.
   const string kShelfItemType_Property = "prop:shelf-item-type";