Add CanCloseDialog to WebDialogDelegate to allow blocking closing of dialog if needed.

ui/web_dialogs/web_dialog_delegate.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_WEB_DIALOGS_WEB_DIALOG_DELEGATE_H_
 #define UI_WEB_DIALOGS_WEB_DIALOG_DELEGATE_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 45 matching lines @@
 
   // Get the size of the dialog.
   virtual void GetDialogSize(gfx::Size* size) const = 0;
 
   // Get the size of the dialog.
   virtual void GetMinimumDialogSize(gfx::Size* size) const;
 
   // Gets the JSON string input to use when showing the dialog.
   virtual std::string GetDialogArgs() const = 0;
 
+  // Returns true to signal that the dialog can be closed. Specialized
+  // WebDialogDelegate subclasses can override this default behavior to allow
+  // the close to be blocked until the user corrects mistakes, accepts an
+  // agreement, etc.
+  virtual bool CanCloseDialog() const;
+
   // A callback to notify the delegate that |source|'s loading state has
   // changed.
   virtual void OnLoadingStateChanged(content::WebContents* source) {}
 
   // A callback to notify the delegate that a web dialog has been shown.
   // |webui| is the WebUI with which the dialog is associated.
   // |render_view_host| is the RenderViewHost for the shown dialog.
   virtual void OnDialogShown(content::WebUI* webui,
                              content::RenderViewHost* render_view_host) {}
 
@@ skipping 44 matching lines @@
 
   // Stores the dialog bounds.
   virtual void StoreDialogSize(const gfx::Size& dialog_size) {}
 
   virtual ~WebDialogDelegate() {}
 };
 
 }  // namespace ui
 
 #endif  // UI_WEB_DIALOGS_WEB_DIALOG_DELEGATE_H_