Add a public API for using an empty sring.

src/api.cc

Index: src/api.cc
===================================================================
--- src/api.cc	(revision 1555)
+++ src/api.cc	(working copy)
@@ -2472,9 +2472,17 @@
 }
 
 
+Local<String> v8::String::Empty() {
+  EnsureInitialized("v8::String::Empty()");
+  LOG_API("String::Empty()");
+  return Utils::ToLocal(i::Factory::empty_symbol());
+}
+
+
 Local<String> v8::String::New(const char* data, int length) {
   EnsureInitialized("v8::String::New()");
   LOG_API("String::New(char)");
+  if (length == 0) return Empty();
   if (length == -1) length = strlen(data);
   i::Handle<i::String> result =
       i::Factory::NewStringFromUtf8(i::Vector<const char>(data, length));
@@ -2503,6 +2511,7 @@
 Local<String> v8::String::New(const uint16_t* data, int length) {
   EnsureInitialized("v8::String::New()");
   LOG_API("String::New(uint16_)");
+  if (length == 0) return Empty();
   if (length == -1) length = TwoByteStringLength(data);
   i::Handle<i::String> result =
       i::Factory::NewStringFromTwoByte(i::Vector<const uint16_t>(data, length));