Fail if an imported file cannot be read.

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 <stdlib.h>
 #include <string.h>
 #include <stdio.h>
 
@@ skipping 113 matching lines @@
     Dart_Handle canon_url = Dart_NewString(canon_url_chars);
     free(const_cast<char*>(canon_url_chars));
 
     return canon_url;
   }
 
   // The tag is either an import or a source tag. Read the file based on the
   // url chars.
   Dart_Handle source = ReadStringFromFile(url_chars);
   if (!Dart_IsValid(source)) {
-    return result;
+    return source;
   }
   if (tag == kImportTag) {
     Dart_Handle new_lib = Dart_LoadLibrary(url, source);
     if (import_builtin_lib && Dart_IsValid(new_lib)) {
       Builtin_ImportLibrary(new_lib);
     }
     return result;
   } else if (tag == kSourceTag) {
     return Dart_LoadSource(library, url, source);
   }
@@ skipping 29 matching lines @@
 
 Dart_Handle LoadSnapshotCreationScript(const char* script_name) {
   Dart_Handle source = ReadStringFromFile(script_name);
   if (!Dart_IsValid(source)) {
     return source;
   }
   Dart_Handle url = Dart_NewString(script_name);
 
   return Dart_LoadScript(url, source, CreateSnapshotLibraryTagHandler);
 }