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

src/spaces-inl.h

Index: src/spaces-inl.h
===================================================================
--- src/spaces-inl.h	(revision 5937)
+++ src/spaces-inl.h	(working copy)
@@ -481,7 +481,7 @@
 }
 
 // -----------------------------------------------------------------------------
-// LargeObjectSpace
+// NewSpace
 
 MaybeObject* NewSpace::AllocateRawInternal(int size_in_bytes,
                                            AllocationInfo* alloc_info) {
@@ -501,6 +501,18 @@
 }
 
 
+template <typename StringType>
+void NewSpace::ShrinkStringAtAllocationBoundary(String* string, int length) {
+  ASSERT(length <= string->length());
+  ASSERT(string->IsSeqString());
+  ASSERT(string->address() + StringType::SizeFor(string->length()) ==
+         allocation_info_.top);
+  allocation_info_.top =
+      string->address() + StringType::SizeFor(length);
+  string->set_length(length);
+}
+
+
 bool FreeListNode::IsFreeListNode(HeapObject* object) {
   return object->map() == Heap::raw_unchecked_byte_array_map()
       || object->map() == Heap::raw_unchecked_one_pointer_filler_map()