mus: Implement interwindow drag and drop

services/ui/public/cpp/window_tree_client.cc

Index: services/ui/public/cpp/window_tree_client.cc
diff --git a/services/ui/public/cpp/window_tree_client.cc b/services/ui/public/cpp/window_tree_client.cc
index c9ef386d8a36d955dcf42e481e75c9695f41bb2c..7d9c37418bd0647a3795a3aa9d01ebb812fe0e37 100644
--- a/services/ui/public/cpp/window_tree_client.cc
+++ b/services/ui/public/cpp/window_tree_client.cc
@@ -16,6 +16,7 @@
 #include "services/ui/common/util.h"
 #include "services/ui/public/cpp/in_flight_change.h"
 #include "services/ui/public/cpp/input_event_handler.h"
+#include "services/ui/public/cpp/window_drop_target.h"
 #include "services/ui/public/cpp/window_manager_delegate.h"
 #include "services/ui/public/cpp/window_observer.h"
 #include "services/ui/public/cpp/window_private.h"
@@ -644,6 +645,33 @@ void WindowTreeClient::StopPointerWatcher() {
   has_pointer_watcher_ = false;
 }
 
+void WindowTreeClient::PerformDragDrop(
+    Window* window,
+    const std::map<std::string, std::vector<uint8_t>>& drag_data,
+    int drag_operation,
+    const gfx::Point& cursor_location,
+    const SkBitmap& bitmap,
+    const base::Callback<void(bool)>& callback) {
+  DCHECK(on_current_drag_finished_.is_null());
+  on_current_drag_finished_ = callback;
+
+  // TODO(erg): Pass |cursor_location| and |bitmap| in PerformDragDrop() when
+  // we start showing an image representation of the drag under he cursor.
+
+  if (window->drop_target()) {
+    // To minimize the number of round trips, copy the drag drop data to our
+    // handler here, instead of forcing mus to send this same data back.
+    window->drop_target()->OnDragStart(drag_data);
+  }
+
+  current_drag_change_ =
+      ScheduleInFlightChange(base::MakeUnique<InFlightDragChange>(window));
+  tree_->PerformDragDrop(
+      current_drag_change_, window->server_id(),
+      mojo::Map<mojo::String, mojo::Array<uint8_t>>::From(drag_data),
+      drag_operation);
+}
+
 void WindowTreeClient::PerformWindowMove(
     Window* window,
     ui::mojom::MoveLoopSource source,
@@ -652,8 +680,8 @@ void WindowTreeClient::PerformWindowMove(
   DCHECK(on_current_move_finished_.is_null());
   on_current_move_finished_ = callback;
 
-  current_move_loop_change_ = ScheduleInFlightChange(
-      base::MakeUnique<InFlightMoveLoopChange>(window));
+  current_move_loop_change_ =
+      ScheduleInFlightChange(base::MakeUnique<InFlightDragChange>(window));
   // Tell the window manager to take over moving us.
   tree_->PerformWindowMove(current_move_loop_change_, window->server_id(),
                            source, cursor_location);
@@ -711,6 +739,11 @@ void WindowTreeClient::RemoveObserver(WindowTreeClientObserver* observer) {
   observers_.RemoveObserver(observer);
 }
 
+void WindowTreeClient::SetCanAcceptDrags(Id window_id, bool can_accept_drags) {
+  DCHECK(tree_);
+  tree_->SetCanAcceptDrags(window_id, can_accept_drags);
+}
+
 void WindowTreeClient::SetCanAcceptEvents(Id window_id,
                                           bool can_accept_events) {
   DCHECK(tree_);
@@ -1057,6 +1090,108 @@ void WindowTreeClient::OnWindowPredefinedCursorChanged(
   WindowPrivate(window).LocalSetPredefinedCursor(cursor);
 }
 
+void WindowTreeClient::OnDragStart(
+    Id window_id,
+    mojo::Map<mojo::String, mojo::Array<uint8_t>> mime_data) {
+  Window* window = GetWindowByServerId(window_id);
+  if (!window)
+    return;
+
+  WindowDropTarget* target = window->drop_target();
+  if (!target)
+    return;
+
+  target->OnDragStart(
+      mime_data.To<std::map<std::string, std::vector<uint8_t>>>());
+}
+
+void WindowTreeClient::OnDragEnter(Id window_id,
+                                   uint32_t key_state,
+                                   const gfx::Point& position,
+                                   uint32_t effect_bitmask,
+                                   const OnDragEnterCallback& callback) {
+  Window* window = GetWindowByServerId(window_id);
+  if (!window) {
+    callback.Run(mojom::kDropEffectNone);
+    return;
+  }
+
+  WindowDropTarget* target = window->drop_target();
+  if (!target) {
+    callback.Run(mojom::kDropEffectNone);
+    return;
+  }
+
+  uint32_t ret = target->OnDragEnter(key_state, position, effect_bitmask);
+  callback.Run(ret);
+}
+
+void WindowTreeClient::OnDragOver(Id window_id,
+                                  uint32_t key_state,
+                                  const gfx::Point& position,
+                                  uint32_t effect_bitmask,
+                                  const OnDragOverCallback& callback) {
+  Window* window = GetWindowByServerId(window_id);
+  if (!window) {
+    callback.Run(mojom::kDropEffectNone);
+    return;
+  }
+
+  WindowDropTarget* target = window->drop_target();
+  if (!target) {
+    callback.Run(mojom::kDropEffectNone);
+    return;
+  }
+
+  uint32_t ret = target->OnDragOver(key_state, position, effect_bitmask);
+  callback.Run(ret);
+}
+
+void WindowTreeClient::OnDragLeave(Id window_id) {
+  Window* window = GetWindowByServerId(window_id);
+  if (!window)
+    return;
+
+  WindowDropTarget* target = window->drop_target();
+  if (!target)
+    return;
+
+  target->OnDragLeave();
+}
+
+void WindowTreeClient::OnDragFinish(Id window_id) {
+  Window* window = GetWindowByServerId(window_id);
+  if (!window)
+    return;
+
+  WindowDropTarget* target = window->drop_target();
+  if (!target)
+    return;
+
+  target->OnDragFinish();
+}
+
+void WindowTreeClient::OnDragDrop(Id window_id,
+                                  uint32_t key_state,
+                                  const gfx::Point& position,
+                                  uint32_t effect_bitmask,
+                                  const OnDragDropCallback& callback) {
+  Window* window = GetWindowByServerId(window_id);
+  if (!window) {
+    callback.Run(mojom::kDropEffectNone);
+    return;
+  }
+
+  WindowDropTarget* target = window->drop_target();
+  if (!target) {
+    callback.Run(mojom::kDropEffectNone);
+    return;
+  }
+
+  uint32_t ret = target->OnDragDrop(key_state, position, effect_bitmask);
+  callback.Run(ret);
+}
+
 void WindowTreeClient::OnChangeCompleted(uint32_t change_id, bool success) {
   std::unique_ptr<InFlightChange> change(std::move(in_flight_map_[change_id]));
   in_flight_map_.erase(change_id);
@@ -1079,6 +1214,15 @@ void WindowTreeClient::OnChangeCompleted(uint32_t change_id, bool success) {
     on_current_move_finished_.Run(success);
     on_current_move_finished_.Reset();
   }
+
+  if (change_id == current_drag_change_) {
+    if (change->window() && change->window()->drop_target())
+      change->window()->drop_target()->OnDragFinish();
+
+    current_drag_change_ = 0;
+    on_current_drag_finished_.Run(success);
+    on_current_drag_finished_.Reset();
+  }
 }
 
 void WindowTreeClient::GetWindowManager(