Add experimental support for external two-byte symbols....

src/heap-inl.h

Index: src/heap-inl.h
===================================================================
--- src/heap-inl.h	(revision 766)
+++ src/heap-inl.h	(working copy)
@@ -38,6 +38,19 @@
 }
 
 
+Object* Heap::AllocateSymbol(Vector<const char> str,
+                             int chars,
+                             uint32_t length_field) {
+  if (global_external_symbol_callback_) {
+    return AllocateExternalSymbol(str, chars);
+  }
+  unibrow::Utf8InputBuffer<> buffer(str.start(),
+                                    static_cast<unsigned>(str.length()));
+  return AllocateInternalSymbol(&buffer, chars, length_field);
+}
+
+
+
 Object* Heap::AllocateRaw(int size_in_bytes,
                           AllocationSpace space,
                           AllocationSpace retry_space) {