MacViews: Implement Tab Dragging

ui/views/cocoa/views_nswindow_delegate.mm

Index: ui/views/cocoa/views_nswindow_delegate.mm
diff --git a/ui/views/cocoa/views_nswindow_delegate.mm b/ui/views/cocoa/views_nswindow_delegate.mm
index 75346a6a8076dadb929abc2f858e5a2cf57e6892..e08ae56e82d9d04e980d395619aa3c1d00dc3e12 100644
--- a/ui/views/cocoa/views_nswindow_delegate.mm
+++ b/ui/views/cocoa/views_nswindow_delegate.mm
@@ -79,6 +79,13 @@
   parent_->OnSizeChanged();
 }
 
+- (void)windowDidMove:(NSNotification*)notification {
+  // Note: windowDidMove: is sent only once at the end of a window drag. There
+  // is also windowWillMove: sent at the start, also once. When the window is
+  // being moved by the WindowServer live updates are not provided.
+  parent_->OnPositionChanged();
+}
+
 - (void)windowDidBecomeKey:(NSNotification*)notification {
   parent_->OnWindowKeyStatusChangedTo(true);
 }