Release the buffer in StringBuilder::toString() and toAtomicString().

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

 /*
  * Copyright (C) 2009, 2010, 2012, 2013 Apple Inc. All rights reserved.
  * Copyright (C) 2012 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.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 98 matching lines @@
             append(string.characters16(), string.length());
     }
 
     void append(UChar c)
     {
         if (m_is8Bit && c <= 0xFF) {
             append(static_cast<LChar>(c));
             return;
         }
         ensureBuffer16(1);
-        m_string = String();
         m_buffer16->append(c);
         ++m_length;
     }
 
     void append(LChar c)
     {
         if (!m_is8Bit) {
             append(static_cast<UChar>(c));
             return;
         }
         ensureBuffer8(1);
-        m_string = String();
         m_buffer8->append(c);
         ++m_length;
     }
 
     void append(char c)
     {
         append(static_cast<LChar>(c));
     }
 
     void append(UChar32 c)
@@ skipping 77 matching lines @@
     }
 
     void ensureBuffer16(unsigned addedSize)
     {
         if (m_is8Bit || !hasBuffer())
             createBuffer16(addedSize);
     }
 
     void createBuffer8(unsigned addedSize);
     void createBuffer16(unsigned addedSize);
-
+    void clearBuffer();
     bool hasBuffer() const { return m_buffer; }
 
     String m_string;
     union {
         Buffer8* m_buffer8;
         Buffer16* m_buffer16;
         void* m_buffer;
     };
     unsigned m_length;
     bool m_is8Bit;
@@ skipping 73 matching lines @@
 inline bool operator==(const StringBuilder& a, const String& b) { return equal(a, b); }
 inline bool operator!=(const StringBuilder& a, const String& b) { return !equal(a, b); }
 inline bool operator==(const String& a, const StringBuilder& b) { return equal(b, a); }
 inline bool operator!=(const String& a, const StringBuilder& b) { return !equal(b, a); }
 
 } // namespace WTF
 
 using WTF::StringBuilder;
 
 #endif // StringBuilder_h