mus: Implement interwindow drag and drop

services/ui/public/cpp/window_drop_target.h

Index: services/ui/public/cpp/window_drop_target.h
diff --git a/services/ui/public/cpp/window_drop_target.h b/services/ui/public/cpp/window_drop_target.h
new file mode 100644
index 0000000000000000000000000000000000000000..dc06bb666b56f280c5b44308ca7ff846f881ff4e
--- /dev/null
+++ b/services/ui/public/cpp/window_drop_target.h
@@ -0,0 +1,40 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef SERVICES_UI_PUBLIC_CPP_WINDOW_DROP_TARGET_H_
+#define SERVICES_UI_PUBLIC_CPP_WINDOW_DROP_TARGET_H_
+
+#include <map>
+#include <vector>
+
+#include "ui/gfx/geometry/point.h"
+
+namespace ui {
+
+// Interface that clients that want to opt-in to receiving drag drop events
+// pass to their mus::Window.
+class WindowDropTarget {
+ public:
+  virtual ~WindowDropTarget() {}
+
+  virtual uint32_t OnDragEnter(
+      std::map<std::string, std::vector<uint8_t>> mime_types,
+      uint32_t key_state,
+      const gfx::Point& position,
+      uint32_t effect_bitmask) = 0;
+
+  virtual uint32_t OnDragOver(uint32_t key_state,
+                              const gfx::Point& position,
+                              uint32_t effect_bitmask) = 0;
+
+  virtual void OnDragLeave() = 0;
+
+  virtual uint32_t OnDragDrop(uint32_t key_state,
+                              const gfx::Point& position,
+                              uint32_t effect_bitmask) = 0;
+};
+
+}  // namespace ui
+
+#endif  // SERVICES_UI_PUBLIC_CPP_WINDOW_DROP_TARGET_H_