Push version 2.5.7 to trunk....

src/handles.cc

Index: src/handles.cc
===================================================================
--- src/handles.cc	(revision 5846)
+++ src/handles.cc	(working copy)
@@ -499,6 +499,10 @@
 
   Handle<FixedArray> array = CalculateLineEnds(src, true);
 
+  if (*array != Heap::empty_fixed_array()) {
+    array->set_map(Heap::fixed_cow_array_map());
+  }
+
   script->set_line_ends(*array);
   ASSERT(script->line_ends()->IsFixedArray());
 }