MacViews: Fix window dragging on Sierra.

ui/views/cocoa/bridged_native_widget.mm

Index: ui/views/cocoa/bridged_native_widget.mm
diff --git a/ui/views/cocoa/bridged_native_widget.mm b/ui/views/cocoa/bridged_native_widget.mm
index ce3731d026165eb42ef39e0b00bafe6953e2fcf9..248e09de35d1fc9c52360eb8fc1e477a7684918b 100644
--- a/ui/views/cocoa/bridged_native_widget.mm
+++ b/ui/views/cocoa/bridged_native_widget.mm
@@ -169,16 +169,20 @@ bool IsPointInResizeArea(NSPoint point, NSWindow* window) {
   return false;
 }
 
+// Routes the |ns_event| to the corresponding BridgedNativeWidget and queries
+// whether the event should be reposted.
 BOOL WindowWantsMouseDownReposted(NSEvent* ns_event) {
-  id delegate = [[ns_event window] delegate];
-  return
-      [delegate
-          respondsToSelector:@selector(shouldRepostPendingLeftMouseDown:)] &&
-      [delegate shouldRepostPendingLeftMouseDown:[ns_event locationInWindow]];
+  DCHECK(views::BridgedNativeWidget::ShouldUseDragEventMonitor());
+
+  views::BridgedNativeWidget* bridge =
+      views::NativeWidgetMac::GetBridgeForNativeWindow([ns_event window]);
+  return bridge && bridge->ShouldRepostPendingLeftMouseDown(ns_event);
 }
 
 // Check if a mouse-down event should drag the window. If so, repost the event.
 NSEvent* RepostEventIfHandledByWindow(NSEvent* ns_event) {
+  DCHECK(views::BridgedNativeWidget::ShouldUseDragEventMonitor());
+
   enum RepostState {
     // Nothing reposted: hit-test new mouse-downs to see if they need to be
     // ignored and reposted after changing draggability.
@@ -253,9 +257,12 @@ NSEvent* RepostEventIfHandledByWindow(NSEvent* ns_event) {
 // To bridge the two models, we monitor mouse-downs with
 // +[NSEvent addLocalMonitorForEventsMatchingMask:handler:]. This receives
 // events after window dragging is handled, so for mouse-downs that land on a
-// draggable point, we cancel the event and repost it at the CGSessionEventTap
-// level so that window dragging will be handled again.
+// draggable point, we cancel the event, make the window draggable and repost it
+// at the CGSessionEventTap level so that window dragging will be handled again.
+// On Mac OS > 10.10, we don't use an event monitor. Instead, we use [NSWindow
+// performWindowDragWithEvent:]. See [NativeWidgetMacNSWindow sendEvent:].
 void SetupDragEventMonitor() {
+  DCHECK(views::BridgedNativeWidget::ShouldUseDragEventMonitor());
   static id monitor = nil;
   if (monitor)
     return;
@@ -338,6 +345,14 @@ gfx::Size BridgedNativeWidget::GetWindowSizeForClientSize(
   return gfx::Size(NSWidth(frame_rect), NSHeight(frame_rect));
 }
 
+// static
+// TODO(karandeepb): Remove usage of drag event monitor once we stop supporting
+// Mac OS 10.10.
+bool BridgedNativeWidget::ShouldUseDragEventMonitor() {
+  return ![NSWindow
+      instancesRespondToSelector:@selector(performWindowDragWithEvent:)];
+}
+
 BridgedNativeWidget::BridgedNativeWidget(NativeWidgetMac* parent)
     : native_widget_mac_(parent),
       focus_manager_(nullptr),
@@ -347,7 +362,9 @@ BridgedNativeWidget::BridgedNativeWidget(NativeWidgetMac* parent)
       in_fullscreen_transition_(false),
       window_visible_(false),
       wants_to_be_visible_(false) {
-  SetupDragEventMonitor();
+  if (BridgedNativeWidget::ShouldUseDragEventMonitor())
+    SetupDragEventMonitor();
+
   DCHECK(parent);
   window_delegate_.reset(
       [[ViewsNSWindowDelegate alloc] initWithBridgedNativeWidget:this]);
@@ -876,26 +893,21 @@ void BridgedNativeWidget::OnWindowKeyStatusChangedTo(bool is_key) {
   }
 }
 
-bool BridgedNativeWidget::ShouldRepostPendingLeftMouseDown(
-    NSPoint location_in_window) {
-  if (!bridged_view_)
+bool BridgedNativeWidget::ShouldDragWindow(NSEvent* event) {
+  if (!bridged_view_ || [event type] != NSLeftMouseDown)
     return false;
 
-  if ([bridged_view_ mouseDownCanMoveWindow]) {
-    // This is a re-post, the movement has already started, so we can make the
-    // window non-draggable again.
-    SetDraggable(false);
-    return false;
-  }
-
+  NSPoint location_in_window = [event locationInWindow];
   if (IsPointInResizeArea(location_in_window, window_))
     return false;
 
   gfx::Point point(location_in_window.x,
                    NSHeight([window_ frame]) - location_in_window.y);
-  bool should_move_window =
-      native_widget_mac()->GetWidget()->GetNonClientComponent(point) ==
-      HTCAPTION;
+
+  if (native_widget_mac()->GetWidget()->GetNonClientComponent(point) !=
+      HTCAPTION) {

[tapted, 2016/11/08 05:03:16]

nit: no curlies

[karandeepb, 2016/11/09 04:44:19]

Done.

+    return false;
+  }
 
   // Check that the point is not obscured by non-content NSViews.
   for (NSView* subview : [[bridged_view_ superview] subviews]) {
@@ -904,12 +916,28 @@ bool BridgedNativeWidget::ShouldRepostPendingLeftMouseDown(
 
     if (![subview mouseDownCanMoveWindow] &&
         NSPointInRect(location_in_window, [subview frame])) {

[tapted, 2016/11/08 05:03:16]

nit: no curlies

[karandeepb, 2016/11/09 04:44:20]

Done.

-      should_move_window = false;
-      break;
+      return false;
     }
   }
 
-  if (!should_move_window)
+  return true;
+}
+
+bool BridgedNativeWidget::ShouldRepostPendingLeftMouseDown(NSEvent* event) {
+  DCHECK(BridgedNativeWidget::ShouldUseDragEventMonitor());
+  DCHECK_EQ(NSLeftMouseDown, [event type]);
+
+  if (!bridged_view_)
+    return false;
+
+  if ([bridged_view_ mouseDownCanMoveWindow]) {
+    // This is a re-post, the movement has already started, so we can make the
+    // window non-draggable again.
+    SetDraggable(false);
+    return false;
+  }
+
+  if (!ShouldDragWindow(event))
     return false;
 
   // Make the window draggable, then return true to repost the event.
@@ -1375,6 +1403,8 @@ NSMutableDictionary* BridgedNativeWidget::GetWindowProperties() const {
 }
 
 void BridgedNativeWidget::SetDraggable(bool draggable) {
+  DCHECK(BridgedNativeWidget::ShouldUseDragEventMonitor());
+
   [bridged_view_ setMouseDownCanMoveWindow:draggable];
   // AppKit will not update its cache of mouseDownCanMoveWindow unless something
   // changes. Previously we tried adding an NSView and removing it, but for some