Better error reporting when passing a non-UTF8 file as script:

runtime/bin/dartutils.cc

 // Copyright (c) 2012, 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 "bin/dartutils.h"
 
 #include "include/dart_api.h"
 #include "include/dart_native_api.h"
 
 #include "platform/assert.h"
@@ skipping 611 matching lines @@
     return Dart_NewApiError(error_msg);
   }
   bool is_snapshot = false;
   const uint8_t *payload = SniffForMagicNumber(buffer, &len, &is_snapshot);
   Dart_Handle returnValue;
   if (is_snapshot) {
     returnValue = Dart_LoadScriptFromSnapshot(payload, len);
   } else {
     Dart_Handle source = Dart_NewStringFromUTF8(buffer, len);
     if (Dart_IsError(source)) {
-      returnValue = source;
+      returnValue = NewError("%s is not a valid UTF-8 script", script_uri);
     } else {
       returnValue = Dart_LoadScript(resolved_script_uri, source, 0, 0);
     }
   }
   free(const_cast<uint8_t *>(buffer));
   return returnValue;
 }
 
 
 Dart_Handle DartUtils::LoadSource(CommandLineOptions* url_mapping,
@@ skipping 433 matching lines @@
       new CObjectString(CObject::NewString(os_error->message()));
   CObjectArray* result = new CObjectArray(CObject::NewArray(3));
   result->SetAt(0, new CObjectInt32(CObject::NewInt32(kOSError)));
   result->SetAt(1, new CObjectInt32(CObject::NewInt32(os_error->code())));
   result->SetAt(2, error_message);
   return result;
 }
 
 }  // namespace bin
 }  // namespace dart