Update comments in core lib showing proper factory syntax.

runtime/lib/error.cc

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "lib/error.h"
 
 #include "vm/bootstrap_natives.h"
 #include "vm/exceptions.h"
 #include "vm/object_store.h"
 #include "vm/runtime_entry.h"
@@ skipping 124 matching lines @@
 
   // Initialize field 'dstType'.
   SetField(type_error, cls, "dstType", dst_type_name);
 
   // Initialize field 'dstName'.
   SetField(type_error, cls, "dstName", dst_name);
 
   // Type errors in the core library may be difficult to diagnose.
   // Print type error information before throwing the error when debugging.
   if (FLAG_print_stack_trace_at_throw) {
-    OS::Print("Type %s is not assignable to type %s of %s.\n",
+    intptr_t line, column;
+    script.GetTokenLocation(location, &line, &column);
+    OS::Print("'%s': Failed type check: line %d pos %d: "
+              "type '%s' is not assignable to type '%s' of '%s'.\n",
+              String::Handle(script.url()).ToCString(),
+              line, column,
               src_type_name.ToCString(),
               dst_type_name.ToCString(),
               dst_name.ToCString());
   }
   // Throw TypeError instance.
   Exceptions::Throw(type_error);
   UNREACHABLE();
 }
 
 
@@ skipping 140 matching lines @@
         dst_type_name = element_type.Name();
       }
       const String& dst_name = String::Handle(String::New(buf));
       ThrowTypeError(location, src_type_name, dst_type_name, dst_name);
       UNREACHABLE();
     }
   }
 }
 
 }  // namespace dart