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

chrome/browser/tab_contents/background_contents.cc

Index: chrome/browser/tab_contents/background_contents.cc
===================================================================
--- chrome/browser/tab_contents/background_contents.cc	(revision 154307)
+++ chrome/browser/tab_contents/background_contents.cc	(working copy)
@@ -94,12 +94,12 @@
 }
 
 // Forward requests to add a new WebContents to our delegate.
-void BackgroundContents::AddNewContents(WebContents* source,
+bool BackgroundContents::AddNewContents(WebContents* source,
                                         WebContents* new_contents,
                                         WindowOpenDisposition disposition,
                                         const gfx::Rect& initial_pos,
                                         bool user_gesture) {
-  delegate_->AddWebContents(
+  return delegate_->AddWebContents(
       new_contents, disposition, initial_pos, user_gesture);
 }