Tab dragging as implemented as a mus API.

components/mus/ws/window_tree.cc

Index: components/mus/ws/window_tree.cc
diff --git a/components/mus/ws/window_tree.cc b/components/mus/ws/window_tree.cc
index 2189fdb92da6212e94132d697ee46b935ed9c34b..eed01e4192adf97217eb3ca41a45d75e0077c83c 100644
--- a/components/mus/ws/window_tree.cc
+++ b/components/mus/ws/window_tree.cc
@@ -407,6 +407,11 @@ void WindowTree::OnWindowManagerCreatedTopLevelWindow(
                               display_id, drawn);
 }
 
+void WindowTree::OnMoveLoopCompleted(uint32_t client_change_id,
+                                     bool completed) {
+  client()->OnMoveLoopCompleted(client_change_id, completed);
+}
+
 void WindowTree::AddActivationParent(const ClientWindowId& window_id) {
   ServerWindow* window = GetWindowByClientId(window_id);
   if (window) {
@@ -1295,7 +1300,8 @@ void WindowTree::OnWindowInputEventAck(uint32_t event_id,
                                        mojom::EventResult result) {
   if (event_ack_id_ == 0 || event_id != event_ack_id_) {
     // TODO(sad): Something bad happened. Kill the client?
-    NOTIMPLEMENTED() << "Wrong event acked.";
+    NOTIMPLEMENTED() << ": Wrong event acked. event_id=" << event_id
+                     << ", event_ack_id_=" << event_ack_id_;
   }
   event_ack_id_ = 0;
 
@@ -1405,6 +1411,52 @@ void WindowTree::GetCursorLocationMemory(
       GetCursorLocationMemory());
 }
 
+void WindowTree::PerformWindowMove(uint32_t change_id,
+                                   Id window_id,
+                                   const gfx::Point& cursor) {
+  // TODO(erg): Should we also ensure that no second client can try to perform

[sky, 2016/06/22 23:47:57]

Yes, as mash won't support it.

+  // a move while another move is in progress?
+
+  ServerWindow* window = GetWindowByClientId(ClientWindowId(window_id));
+  bool success = window && access_policy_->CanInitiateMoveLoop(window);
+  if (!success) {

[sky, 2016/06/22 23:47:57]

You should also fail if ShouldRouteToWindowManager returns false.

+    // We need to fail this move loop change, otherwise the client will just be
+    // waiting for |change_id|.
+    OnMoveLoopCompleted(change_id, false);
+    return;
+  }
+
+  WindowManagerState* wms = display_manager()
+                                ->GetWindowManagerAndDisplay(window)
+                                .window_manager_state;

[sky, 2016/06/22 23:47:57]

Sorry, I changed this around. You'll want:

    WindowManagerDisplayRoot* display_root =
        GetWindowManagerDisplayRoot(window);
    WindowTree* wm_tree = display_root->window_manager_state();

+
+  // When we perform a window move loop, we give the window manager non client
+  // capture. Because of how the capture public interface currently works,
+  // SetCapture() will check whether the mouse cursor is currently in the
+  // non-client area and if so, will redirect messages to the window
+  // manager. (And normal window movement relies on this behaviour.)
+  wms->SetCapture(window, true);

[sky, 2016/06/22 23:47:57]

true should be the id() of the WindowTree from WindowManagerState.

+
+  const uint32_t wm_change_id =
+      window_server_->GenerateWindowManagerChangeId(this, change_id);
+  wms->tree()->window_manager_internal_->WmPerformMoveLoop(
+      wm_change_id, wms->tree()->ClientWindowIdForWindow(window).id, cursor);
+}
+
+void WindowTree::CancelWindowMove(Id window_id) {
+  ServerWindow* window = GetWindowByClientId(ClientWindowId(window_id));
+  bool success = window && access_policy_->CanInitiateMoveLoop(window);
+  if (!success)
+    return;
+
+  WindowManagerState* wms = display_manager()
+                                ->GetWindowManagerAndDisplay(window)
+                                .window_manager_state;
+
+  wms->tree()->window_manager_internal_->WmCancelMoveLoop(
+      wms->tree()->ClientWindowIdForWindow(window).id);
+}
+
 void WindowTree::AddAccelerator(uint32_t id,
                                 mojom::EventMatcherPtr event_matcher,
                                 const AddAcceleratorCallback& callback) {
@@ -1497,6 +1549,27 @@ void WindowTree::OnWmCreatedTopLevelWindow(uint32_t change_id,
   window_server_->WindowManagerCreatedTopLevelWindow(this, change_id, window);
 }
 
+void WindowTree::OnWmMoveLoopCompleted(uint32_t change_id,
+                                       Id transport_window_id,
+                                       bool succeeded) {
+  WindowManagerState* wms = GetWindowManagerStateForWindowManager();
+  if (wms) {
+    ServerWindow* window =
+        GetWindowByClientId(ClientWindowId(transport_window_id));
+
+    if (window && window->id().client_id != id_) {
+      window_server_->WindowManagerSentBogusMessage();
+      window = nullptr;
+    } else {
+      // Clear the implicit capture.
+      wms->SetCapture(nullptr, false);
+    }
+
+    window_server_->WindowManagerCompletedMoveLoop(change_id, window,
+                                                   succeeded);
+  }
+}
+
 bool WindowTree::HasRootForAccessPolicy(const ServerWindow* window) const {
   return HasRoot(window);
 }