Allocate space in StringBuilder for m_string and the new bytes.

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 97 matching lines @@
         else
             append(string.characters16(), string.length());
     }
 
     void append(UChar c)
     {
         if (m_is8Bit && c <= 0xFF) {
             append(static_cast<LChar>(c));
             return;
         }
-        ensureBuffer16();
+        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();
+        ensureBuffer8(1);
         m_string = String();
         m_buffer8->append(c);
         ++m_length;
     }
 
     void append(char c)
     {
         append(static_cast<LChar>(c));
     }
 
@@ skipping 57 matching lines @@
         DCHECK(m_buffer16);
         return m_buffer16->data();
     }
 
     bool is8Bit() const { return m_is8Bit; }
 
     void clear();
     void swap(StringBuilder&);
 
 private:
-    typedef Vector<LChar, 16> Buffer8;
-    typedef Vector<UChar, 16> Buffer16;
+    static const unsigned kInlineBufferSize = 16;
+    static unsigned initialBufferSize() { return kInlineBufferSize; }

[esprehn, 2016/06/30 23:23:15]

You have to have a method since using kInlineBufferSize in std::max doesn't work
since it tries to take a reference... silly stl.

 
-    void ensureBuffer8()
+    typedef Vector<LChar, kInlineBufferSize> Buffer8;
+    typedef Vector<UChar, kInlineBufferSize> Buffer16;
+
+    void ensureBuffer8(unsigned addedSize)
     {
         DCHECK(m_is8Bit);
         if (!hasBuffer())
-            createBuffer8();
+            createBuffer8(addedSize);
     }
 
-    void ensureBuffer16()
+    void ensureBuffer16(unsigned addedSize)
     {
         if (m_is8Bit || !hasBuffer())
-            createBuffer16();
+            createBuffer16(addedSize);
     }
 
-    void createBuffer8();
-    void createBuffer16();
+    void createBuffer8(unsigned addedSize);
+    void createBuffer16(unsigned addedSize);
 
     bool hasBuffer() const { return m_buffer; }
 
     String m_string;
     union {
         Buffer8* m_buffer8;
         Buffer16* m_buffer16;
         void* m_buffer;
     };
     unsigned m_length;
@@ skipping 74 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