Ignore non-ASCII headers in the mimeHandlerPrivate API.

extensions/common/api/mime_handler_private.idl

 // Copyright 2015 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.
 
 // Mime handler API.
 [nodoc] namespace mimeHandlerPrivate {
   dictionary StreamInfo {
     // The MIME type of the intercepted URL request.
     DOMString mimeType;
 
     // The original URL that was intercepted.
     DOMString originalUrl;
 
     // The URL that the stream can be read from.
     DOMString streamUrl;
 
     // The ID of the tab that opened the stream. If the stream is not opened in
     // a tab, it will be -1.
     long tabId;
 
     // The HTTP response headers of the intercepted request stored as a
     // dictionary mapping header name to header value. If a header name appears
     // multiple times, the header values are merged in the dictionary and
-    // separated by a ", ".
+    // separated by a ", ". Non-ASCII headers are dropped.
     object responseHeaders;
 
     // Whether the stream is embedded within another document.
     boolean embedded;
   };
 
   callback AbortCallback = void ();
   callback GetStreamDetailsCallback = void (StreamInfo streamInfo);
 
   interface Functions {
     // Returns the StreamInfo for the stream for this context if there is one.
     [nocompile] static void getStreamInfo(GetStreamDetailsCallback callback);
 
     // Aborts the stream for this context if there is one.
     [nocompile] static void abortStream(optional AbortCallback callback);
   };
 };