Pass result of blockage across content API when new tab blocked.

ui/web_dialogs/web_dialog_web_contents_delegate.cc

Index: ui/web_dialogs/web_dialog_web_contents_delegate.cc
===================================================================
--- ui/web_dialogs/web_dialog_web_contents_delegate.cc	(revision 154307)
+++ ui/web_dialogs/web_dialog_web_contents_delegate.cc	(working copy)
@@ -39,12 +39,12 @@
   return handler_->OpenURLFromTab(browser_context_, source, params);
 }
 
-void WebDialogWebContentsDelegate::AddNewContents(
+bool WebDialogWebContentsDelegate::AddNewContents(
     WebContents* source, WebContents* new_contents,
     WindowOpenDisposition disposition, const gfx::Rect& initial_pos,
     bool user_gesture) {
-  handler_->AddNewContents(browser_context_, source, new_contents, disposition,
-                           initial_pos, user_gesture);
+  return handler_->AddNewContents(browser_context_, source, new_contents,
+                                  disposition, initial_pos, user_gesture);
 }
 
 bool WebDialogWebContentsDelegate::IsPopupOrPanel(