Improve error handling in the process library.

runtime/bin/process_script.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.
 
 // Handle dart scripts.
 
-#include <assert.h>
 #include <stdlib.h>
 #include <string.h>
 #include <stdio.h>
 
 #include "include/dart_api.h"
 
 #include "bin/builtin.h"
 #include "bin/file.h"
 #include "bin/globals.h"
 #include "bin/process_script.h"
@@ skipping 131 matching lines @@
 Dart_Result LoadScript(const char* script_name) {
   Dart_Result result = ReadStringFromFile(script_name);
   if (!Dart_IsValidResult(result)) {
     return result;
   }
   Dart_Handle source = Dart_GetResult(result);
   Dart_Handle url = Dart_NewString(script_name);
 
   return Dart_LoadScript(url, source, LibraryTagHandler);
 }