mash: Serialize ShelfIDs for property conversion and transport.

ash/wm/overview/window_selector_unittest.cc

Index: ash/wm/overview/window_selector_unittest.cc
diff --git a/ash/wm/overview/window_selector_unittest.cc b/ash/wm/overview/window_selector_unittest.cc
index 2e437ff82dad42a1e0ec9d000dd71aceed057c36..6a46fe0b9ce59a82a7ca368adf0201f5f3554485 100644
--- a/ash/wm/overview/window_selector_unittest.cc
+++ b/ash/wm/overview/window_selector_unittest.cc
@@ -148,7 +148,8 @@ class WindowSelectorTest : public test::AshTestBase {
     aura::Window* window = CreateTestWindowInShellWithDelegateAndType(
         nullptr, ui::wm::WINDOW_TYPE_PANEL, 0, bounds);
     static int id = 0;
-    window->SetProperty(kShelfIDKey, new ShelfID(base::IntToString(id++)));
+    std::string shelf_id(ShelfID(base::IntToString(id++)).Serialize());
+    window->SetProperty(kShelfIDKey, new std::string(shelf_id));
     window->SetProperty(aura::client::kTopViewInset, kHeaderHeight);
     shelf_view_test()->RunMessageLoopUntilAnimationsDone();
     return window;