Bring up the service isolate and use it for package resolution in gen_snapshot

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_tools_api.h"
 #include "include/dart_native_api.h"
 
@@ skipping 645 matching lines @@
       result = Dart_SetField(builtin_lib,
                              NewString("_traceLoading"), Dart_True());
       RETURN_IF_ERROR(result);
     }
     // Set current working directory.
     result = SetWorkingDirectory(builtin_lib);
     RETURN_IF_ERROR(result);
     // Wait for the service isolate to initialize the load port.
     Dart_Port load_port = Dart_ServiceWaitForLoadPort();
     if (load_port == ILLEGAL_PORT) {
-      return NewDartUnsupportedError("Service did not return load port.");
+      return Dart_NewUnhandledExceptionError(
+          NewDartUnsupportedError("Service did not return load port."));
     }
     result = Builtin::SetLoadPort(load_port);
     RETURN_IF_ERROR(result);
   }
 
   // Set up package root if specified.
   if (package_root != NULL) {
     ASSERT(package_map == NULL);
     ASSERT(packages_file == NULL);
     result = NewString(package_root);
@@ skipping 594 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