Allow data URLs to trigger downloads, as they do in Firefox....

net/base/data_url.cc

 // Copyright (c) 2006-2008 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.
 
 // NOTE: based loosely on mozilla's nsDataChannel.cpp
 
 #include <algorithm>
 
 #include "net/base/data_url.h"
 
@@ skipping 42 matching lines @@
         charset->assign(it + sizeof(kCharsetTag)-1, comma);
     }
   }
 
   // fallback to defaults if nothing specified in the URL:
   if (mime_type->empty())
     mime_type->assign("text/plain");
   if (charset->empty())
     charset->assign("US-ASCII");
 
+  // The caller may not be interested in receiving the data.
+  if (!data)
+    return true;
+
   // Preserve spaces if dealing with text or xml input, same as mozilla:
   //   https://bugzilla.mozilla.org/show_bug.cgi?id=138052
   // but strip them otherwise:
   //   https://bugzilla.mozilla.org/show_bug.cgi?id=37200
   // (Spaces in a data URL should be escaped, which is handled below, so any
   // spaces now are wrong. People expect to be able to enter them in the URL
   // bar for text, and it can't hurt, so we allow it.)
   std::string temp_data = std::string(comma + 1, end);
 
   // For base64, we may have url-escaped whitespace which is not part
@@ skipping 20 matching lines @@
   }
 
   if (base64_encoded)
     return base::Base64Decode(temp_data, data);
 
   temp_data.swap(*data);
   return true;
 }
 
 }  // namespace net