mash: Move ShelfWindowWatcher[ItemDelegate] to ash/common.

ash/aura/wm_window_aura.cc

Index: ash/aura/wm_window_aura.cc
diff --git a/ash/aura/wm_window_aura.cc b/ash/aura/wm_window_aura.cc
index 23a1556ac094bf00ee9298df981e2303bd5e49c4..f6eda0933978aad10e9b9b425613877160e07fc1 100644
--- a/ash/aura/wm_window_aura.cc
+++ b/ash/aura/wm_window_aura.cc
@@ -291,6 +291,16 @@ ShelfItemDetails* WmWindowAura::GetShelfItemDetails() {
   return window_->GetProperty(kShelfItemDetailsKey);
 }
 
+void WmWindowAura::SetShelfItemDetails(const ShelfItemDetails& details) {
+  // |item_details| is owned by |window_|.
+  ShelfItemDetails* item_details = new ShelfItemDetails(details);
+  window_->SetProperty(kShelfItemDetailsKey, item_details);
+}
+
+void WmWindowAura::ClearShelfItemDetails() {
+  window_->ClearProperty(kShelfItemDetailsKey);
+}
+
 const wm::WindowState* WmWindowAura::GetWindowState() const {
   return ash::wm::GetWindowState(window_);
 }