MacViews: Implemented Drag & Drop

ui/views/cocoa/bridged_content_view.h

Index: ui/views/cocoa/bridged_content_view.h
diff --git a/ui/views/cocoa/bridged_content_view.h b/ui/views/cocoa/bridged_content_view.h
index 20111a8bf6b229fe91a147d51dea73e71118fa60..936545166a13e599418b9b87aaf64e7bed6ece8a 100644
--- a/ui/views/cocoa/bridged_content_view.h
+++ b/ui/views/cocoa/bridged_content_view.h
@@ -22,8 +22,9 @@ class View;
 // The NSView that sits as the root contentView of the NSWindow, whilst it has
 // a views::RootView present. Bridges requests from Cocoa to the hosted
 // views::View.
-@interface BridgedContentView
-    : ToolTipBaseView<NSTextInputClient, NSUserInterfaceValidations> {
+@interface BridgedContentView : ToolTipBaseView<NSTextInputClient,
+                                                NSUserInterfaceValidations,
+                                                NSDraggingSource> {
  @private
   // Weak. The hosted RootView, owned by hostedView_->GetWidget().
   views::View* hostedView_;