Use StringView for String::append and ::insert.

third_party/WebKit/Source/wtf/text/WTFString.h

 /*
  * (C) 1999 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012, 2013 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 202 matching lines @@
     bool startsWith(const StringView& prefix, TextCaseSensitivity caseSensitivity = TextCaseSensitive) const
         { return m_impl ? DISPATCH_CASE_OP(caseSensitivity, m_impl->startsWith, (prefix)) : prefix.isEmpty(); }
     bool startsWith(UChar character) const
         { return m_impl ? m_impl->startsWith(character) : false; }
 
     bool endsWith(const StringView& suffix, TextCaseSensitivity caseSensitivity = TextCaseSensitive) const
         { return m_impl ? DISPATCH_CASE_OP(caseSensitivity, m_impl->endsWith, (suffix)) : suffix.isEmpty(); }
     bool endsWith(UChar character) const
         { return m_impl ? m_impl->endsWith(character) : false; }
 
-    void append(const String&);
+    void append(const StringView&);
     void append(LChar);
     void append(char c) { append(static_cast<LChar>(c)); }
     void append(UChar);
-    void append(const LChar*, unsigned length);
-    void append(const char* charactersToAppend, unsigned length) { append(reinterpret_cast<const LChar*>(charactersToAppend), length); }
-    void append(const UChar*, unsigned length);
-    void insert(const String&, unsigned pos);
-    void insert(const LChar*, unsigned length, unsigned pos);
-    void insert(const UChar*, unsigned length, unsigned pos);
+    void insert(const StringView&, unsigned pos);
 
     String& replace(UChar a, UChar b)
     {
         if (m_impl)
             m_impl = m_impl->replace(a, b);
         return *this;
     }
     String& replace(UChar a, const String& b)
     {
         if (m_impl)
@@ skipping 354 matching lines @@
 using WTF::emptyString16Bit;
 using WTF::append;
 using WTF::charactersAreAllASCII;
 using WTF::equal;
 using WTF::find;
 using WTF::isAllSpecialCharacters;
 using WTF::isSpaceOrNewline;
 
 #include "wtf/text/AtomicString.h"
 #endif // WTFString_h