MacViews: Fix window dragging on Sierra.

ui/views/cocoa/native_widget_mac_nswindow.mm

Index: ui/views/cocoa/native_widget_mac_nswindow.mm
diff --git a/ui/views/cocoa/native_widget_mac_nswindow.mm b/ui/views/cocoa/native_widget_mac_nswindow.mm
index f3ccb522652a85af015b7bf64c9c3651ae8d91dd..0f077fe12b65c90ba4126e6ba6496e134b0071f7 100644
--- a/ui/views/cocoa/native_widget_mac_nswindow.mm
+++ b/ui/views/cocoa/native_widget_mac_nswindow.mm
@@ -5,6 +5,7 @@
 #import "ui/views/cocoa/native_widget_mac_nswindow.h"
 
 #include "base/mac/foundation_util.h"
+#import "base/mac/sdk_forward_declarations.h"
 #import "ui/views/cocoa/bridged_native_widget.h"
 #import "ui/base/cocoa/user_interface_item_command_handler.h"
 #import "ui/views/cocoa/views_nswindow_delegate.h"
@@ -107,14 +108,32 @@ - (BOOL)hasKeyAppearance {
   return [super hasKeyAppearance];
 }
 
-// Override sendEvent to allow key events to be forwarded to a toolkit-views
-// menu while it is active, and while still allowing any native subview to
-// retain firstResponder status.
+// Override sendEvent to intercept window drag events and allow key events to be
+// forwarded to a toolkit-views menu while it is active, and while still
+// allowing any native subview to retain firstResponder status.
 - (void)sendEvent:(NSEvent*)event {
   // Let CommandDispatcher check if this is a redispatched event.
   if ([commandDispatcher_ preSendEvent:event])
     return;
 
+  // If a window drag event monitor is not used, query the BridgedNativeWidget
+  // to decide if a window drag should be performed.
+  if (!views::BridgedNativeWidget::ShouldUseDragEventMonitor()) {
+    views::BridgedNativeWidget* bridge =
+        views::NativeWidgetMac::GetBridgeForNativeWindow(self);
+
+    if (bridge && bridge->ShouldDragWindow(event)) {
+      // Using performWindowDragWithEvent: does not generate a
+      // NSWindowWillMoveNotification. Hence post one.
+      [[NSNotificationCenter defaultCenter]
+          postNotificationName:NSWindowWillMoveNotification
+                        object:self];
+
+      [self performWindowDragWithEvent:event];
+      return;
+    }
+  }
+
   NSEventType type = [event type];
   if ((type != NSKeyDown && type != NSKeyUp) || ![self hasViewsMenuActive]) {
     [super sendEvent:event];