Tab dragging as implemented as a mus API.

ash/mus/frame/move_event_handler.cc

Index: ash/mus/frame/move_event_handler.cc
diff --git a/ash/mus/frame/move_event_handler.cc b/ash/mus/frame/move_event_handler.cc
index b903dce5d7465a89418e7ed88a6cf6e7d0ca7f4b..d186cdc0a00847a38bfcee8ca740b459847d272a 100644
--- a/ash/mus/frame/move_event_handler.cc
+++ b/ash/mus/frame/move_event_handler.cc
@@ -5,6 +5,7 @@
 #include "ash/mus/frame/move_event_handler.h"
 
 #include "ash/mus/bridge/wm_window_mus.h"
+#include "base/lazy_instance.h"
 #include "components/mus/public/cpp/window.h"
 #include "components/mus/public/cpp/window_manager_delegate.h"
 #include "components/mus/public/interfaces/cursor.mojom.h"
@@ -16,6 +17,9 @@ namespace ash {
 namespace mus {
 namespace {
 
+base::LazyInstance<std::map<WmWindow*, MoveEventHandler*>> g_live_handlers =
+    LAZY_INSTANCE_INITIALIZER;
+
 ::mus::mojom::Cursor CursorForWindowComponent(int window_component) {
   switch (window_component) {
     case HTBOTTOM:
@@ -39,6 +43,12 @@ namespace {
   }
 }
 
+void OnMoveLoopCompleted(const base::Callback<void(bool success)>& end_closure,
+                         wm::WmToplevelWindowEventHandler::DragResult result) {
+  end_closure.Run(result ==
+                  wm::WmToplevelWindowEventHandler::DragResult::SUCCESS);
+}
+
 }  // namespace
 
 MoveEventHandler::MoveEventHandler(
@@ -51,12 +61,37 @@ MoveEventHandler::MoveEventHandler(
       toplevel_window_event_handler_(wm_window_->GetShell()) {
   root_window_->AddObserver(this);
   root_window_->AddPreTargetHandler(this);
+
+  DCHECK(g_live_handlers.Get().find(wm_window_) == g_live_handlers.Get().end());
+  g_live_handlers.Get()[wm_window_] = this;
 }
 
 MoveEventHandler::~MoveEventHandler() {
   Detach();
 }
 
+// static
+MoveEventHandler* MoveEventHandler::GetForWindow(WmWindow* wm_window) {
+  auto it = g_live_handlers.Get().find(wm_window);
+  if (it != g_live_handlers.Get().end())
+    return it->second;
+  return nullptr;
+}
+
+void MoveEventHandler::AttemptToStartDrag(
+    const gfx::Point& point_in_parent,
+    int window_component,
+    const base::Callback<void(bool success)>& end_closure) {
+  toplevel_window_event_handler_.AttemptToStartDrag(
+      wm_window_, point_in_parent, window_component,
+      aura::client::WINDOW_MOVE_SOURCE_MOUSE,
+      base::Bind(&OnMoveLoopCompleted, end_closure));
+}
+
+void MoveEventHandler::RevertDrag() {
+  toplevel_window_event_handler_.RevertDrag();
+}
+
 void MoveEventHandler::Detach() {
   if (!root_window_)
     return;
@@ -64,6 +99,8 @@ void MoveEventHandler::Detach() {
   root_window_->RemoveObserver(this);
   root_window_->RemovePreTargetHandler(this);
   root_window_ = nullptr;
+
+  g_live_handlers.Get().erase(wm_window_);
 }
 
 void MoveEventHandler::OnMouseEvent(ui::MouseEvent* event) {