MacViews: Implemented Drag & Drop

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 1c9560f2e8834aeb19225abd760819145854b361..a85b1325780dafe80cce8be5b3e4981d14f4a2ba 100644
--- a/ui/views/cocoa/bridged_native_widget.mm
+++ b/ui/views/cocoa/bridged_native_widget.mm
@@ -24,6 +24,7 @@
 #import "ui/gfx/mac/coordinate_conversion.h"
 #import "ui/gfx/mac/nswindow_frame_controls.h"
 #import "ui/views/cocoa/bridged_content_view.h"
+#import "ui/views/cocoa/drag_drop_client_mac.h"
 #import "ui/views/cocoa/cocoa_mouse_capture.h"
 #include "ui/views/cocoa/tooltip_manager_mac.h"
 #import "ui/views/cocoa/views_nswindow_delegate.h"
@@ -463,6 +464,7 @@ void BridgedNativeWidget::Init(base::scoped_nsobject<NSWindow> window,
   // native on Mac, so nothing should ever want one in Widget form.
   DCHECK_NE(params.type, Widget::InitParams::TYPE_TOOLTIP);
   tooltip_manager_.reset(new TooltipManagerMac(this));
+  drag_drop_client_.reset(new DragDropClientMac(this));
 }
 
 void BridgedNativeWidget::SetFocusManager(FocusManager* focus_manager) {
@@ -527,6 +529,8 @@ void BridgedNativeWidget::SetRootView(views::View* view) {
 
   if (view) {
     bridged_view_.reset([[BridgedContentView alloc] initWithView:view]);
+    drag_drop_client_->SetRootView(view);

[tapted, 2016/05/31 11:49:58]

ooh - so we should remove the reference to |view| in drag_drop_client_ when
something calls SetRootView(nullptr), otherwise it might be referring to deleted
data. Even better, we should just reset drag_drop_client_

I think the best way to do this is to pass |view| into the DragDropClient
constructor. That means:

move the `drag_drop_client_.reset(new DragDropClientMac(this));` call in Init()
down to here (and also pass |view| -- remove DragDropClientMac::SetRootView

Then add a call to `drag_drop_client_.reset()` up above, just before the
[bridged_view_ clearView] call.

[spqchan, 2016/05/31 23:06:12]

Done. Note, I didn't add drag_drop_client_.reset() because it actually conflicts
with the implementation for ViewRemoved(). 

+
     // Objective C initializers can return nil. However, if |view| is non-NULL
     // this should be treated as an error and caught early.
     CHECK(bridged_view_);