Ignore non-ASCII headers in the mimeHandlerPrivate API.

extensions/common/api/mime_handler.mojom

 // 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.
 
 module extensions.mime_handler;
 
 // Information about a stream.
 struct StreamInfo {
   // The MIME type of the intercepted URL request.
   string mime_type;
 
   // The original URL that was intercepted.
   string original_url;
 
   // The URL that the stream can be read from.
   string stream_url;
 
   // The ID of the tab that opened the stream. If the stream is not opened in a
   // tab, it will be -1.
   int32 tab_id;
 
   // 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
-  // ",".
+  // ",". Non-ASCII headers are dropped.
   map<string, string> response_headers;
 
   // Whether the stream is embedded within another document.
   bool embedded;
 };
 
 interface MimeHandlerService {
   // Returns information about the stream associated with this service instance.
   // If the stream has been aborted, |stream_info| will be null.
   GetStreamInfo() => (StreamInfo? stream_info);
 
   // Aborts the stream associated with this service instance. This is an
   // idempotent operation.
   AbortStream() => ();
 };