Add render frame observer for CopylessPaste

third_party/WebKit/Source/modules/document_metadata/CopylessPasteExtractor.h

 // Copyright 2017 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.
 
 #ifndef CopylessPasteExtractor_h
 #define CopylessPasteExtractor_h
 
 #include "modules/ModulesExport.h"
 #include "wtf/text/WTFString.h"
 
 namespace blink {
 
 class Document;
 
 // Extract structured metadata (currently schema.org in JSON-LD) for the
 // Copyless Paste feature. The extraction must be done after the document
 // has finished parsing.
 class MODULES_EXPORT CopylessPasteExtractor final {
  public:
-  static String extract(Document&);
+  static void extract(Document&);
+  // Visible for testing
+  static String metadata(Document&);
 };
 
 }  // namespace blink
 
 #endif  // CopylessPasteExtractor_h