Second step towards loading the core library scripts directly from the sources

runtime/vm/heap.cc

Index: runtime/vm/heap.cc
===================================================================
--- runtime/vm/heap.cc	(revision 22375)
+++ runtime/vm/heap.cc	(working copy)
@@ -321,7 +321,7 @@
   intptr_t len = OS::SNPrint(NULL, 0, format, isolate->name(), reason);
   char* filename = isolate->current_zone()->Alloc<char>(len + 1);
   OS::SNPrint(filename, len + 1, format, isolate->name(), reason);
-  void* file = (*file_open)(filename);
+  void* file = (*file_open)(filename, true);
   if (file != NULL) {
     Profile(file_write, file);
     (*file_close)(file);