feat: 'will-move' event for windows.

atom/browser/api/atom_api_top_level_window.cc

@@ -205,6 +205,13 @@ void TopLevelWindow::OnWindowResize() {
   Emit("resize");
 }
 
+void TopLevelWindow::OnWindowWillMove(const gfx::Rect& new_bounds,
+                                      bool* prevent_default) {
+  if (Emit("will-move", new_bounds)) {
+    *prevent_default = true;
+  }
+}
+
 void TopLevelWindow::OnWindowMove() {
   Emit("move");
 }

atom/browser/api/atom_api_top_level_window.h

@@ -63,6 +63,8 @@ class TopLevelWindow : public mate::TrackableObject<TopLevelWindow>,
   void OnWindowWillResize(const gfx::Rect& new_bounds,
                           bool* prevent_default) override;
   void OnWindowResize() override;
+  void OnWindowWillMove(const gfx::Rect& new_bounds,
+                        bool* prevent_default) override;
   void OnWindowMove() override;
   void OnWindowMoved() override;
   void OnWindowScrollTouchBegin() override;

atom/browser/native_window.cc

@@ -464,6 +464,12 @@ void NativeWindow::NotifyWindowWillResize(const gfx::Rect& new_bounds,
     observer.OnWindowWillResize(new_bounds, prevent_default);
 }
 
+void NativeWindow::NotifyWindowWillMove(const gfx::Rect& new_bounds,
+                                        bool* prevent_default) {
+  for (NativeWindowObserver& observer : observers_)
+    observer.OnWindowWillMove(new_bounds, prevent_default);
+}
+
 void NativeWindow::NotifyWindowResize() {
   for (NativeWindowObserver& observer : observers_)
     observer.OnWindowResize();

atom/browser/native_window.h

@@ -239,6 +239,7 @@ class NativeWindow : public base::SupportsUserData,
   void NotifyWindowWillResize(const gfx::Rect& new_bounds,
                               bool* prevent_default);
   void NotifyWindowResize();
+  void NotifyWindowWillMove(const gfx::Rect& new_bounds, bool* prevent_default);
   void NotifyWindowMoved();
   void NotifyWindowScrollTouchBegin();
   void NotifyWindowScrollTouchEnd();

atom/browser/native_window_observer.h

@@ -70,6 +70,8 @@ class NativeWindowObserver {
   virtual void OnWindowWillResize(const gfx::Rect& new_bounds,
                                   bool* prevent_default) {}
   virtual void OnWindowResize() {}
+  virtual void OnWindowWillMove(const gfx::Rect& new_bounds,
+                                bool* prevent_default) {}
   virtual void OnWindowMove() {}
   virtual void OnWindowMoved() {}
   virtual void OnWindowScrollTouchBegin() {}

atom/browser/native_window_views_win.cc

@@ -207,9 +207,16 @@ bool NativeWindowViews::PreHandleMSG(UINT message,
       return false;
     }
     case WM_MOVING: {
-      if (!movable_)
+      bool prevent_default = false;
+      NotifyWindowWillMove(gfx::Rect(*reinterpret_cast<RECT*>(l_param)),
+                           &prevent_default);
+      if (!movable_ || prevent_default) {
         ::GetWindowRect(GetAcceleratedWidget(),
                         reinterpret_cast<RECT*>(l_param));
+        return true;  // Tells Windows that the Move is handled. If not true,
+                      // frameless windows can be moved using
+                      // -webkit-app-region: drag elements.
+      }
       return false;
     }
     case WM_MOVE: {

docs/api/browser-window.md

@@ -505,6 +505,17 @@ Note that this is only emitted when the window is being resized manually. Resizi
 
 Emitted after the window has been resized.
 
+#### Event: 'will-move' _Windows_
+
+Returns:
+
+* `event` Event
+* `newBounds` [`Rectangle`](structures/rectangle.md) - Location the window is being moved to.
+
+Emitted before the window is moved. Calling `event.preventDefault()` will prevent the window from being moved.
+
+Note that this is only emitted when the window is being resized manually. Resizing the window with `setBounds`/`setSize` will not emit this event.
+
 #### Event: 'move'
 
 Emitted when the window is being moved to a new position.