Speed up quoting of JSON strings by allocating a string that is big enough...

src/spaces.h

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1625 matching lines @@
   // respective semispace (not necessarily below the allocation pointer of the
   // semispace).
   bool ToSpaceContains(Object* o) { return to_space_.Contains(o); }
   bool FromSpaceContains(Object* o) { return from_space_.Contains(o); }
 
   bool ToSpaceContains(Address a) { return to_space_.Contains(a); }
   bool FromSpaceContains(Address a) { return from_space_.Contains(a); }
 
   virtual bool ReserveSpace(int bytes);
 
+  // Resizes a sequential string which must be the most recent thing that was
+  // allocated in new space.
+  template <typename StringType>
+  inline void ShrinkStringAtAllocationBoundary(String* string, int len);
+
 #ifdef ENABLE_HEAP_PROTECTION
   // Protect/unprotect the space by marking it read-only/writable.
   virtual void Protect();
   virtual void Unprotect();
 #endif
 
 #ifdef DEBUG
   // Verify the active semispace.
   virtual void Verify();
   // Print the active semispace.
@@ skipping 687 matching lines @@
 
  private:
   LargeObjectChunk* current_;
   HeapObjectCallback size_func_;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_SPACES_H_