Provide a std::vector compliant empty() method for WebVector.

third_party/WebKit/Source/core/loader/DocumentLoader.cpp

 /*
  * Copyright (C) 2006, 2007, 2008 Apple Inc. All rights reserved.
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 1008 matching lines @@
         frame->securityContext()->getSecurityOrigin());
   }
   frame->securityContext()->initializeFeaturePolicy(
       parsedHeader, containerPolicy, parentFeaturePolicy);
 
   for (auto& message : messages) {
     document->addConsoleMessage(
         ConsoleMessage::create(OtherMessageSource, ErrorMessageLevel,
                                "Error with Feature-Policy header: " + message));
   }
-  if (!parsedHeader.isEmpty())
+  if (!parsedHeader.empty())
     frame->client()->didSetFeaturePolicyHeader(parsedHeader);
 }
 
 void DocumentLoader::installNewDocument(
     const DocumentInit& init,
     const AtomicString& mimeType,
     const AtomicString& encoding,
     InstallNewDocumentReason reason,
     ParserSynchronizationPolicy parsingPolicy,
     const KURL& overridingURL) {
@@ skipping 42 matching lines @@
                      InstallNewDocumentReason::kJavascriptURL,
                      ForceSynchronousParsing, KURL());
   if (!source.isNull())
     m_writer->appendReplacingData(source);
   endWriting();
 }
 
 DEFINE_WEAK_IDENTIFIER_MAP(DocumentLoader);
 
 }  // namespace blink