Fixed assert causing crash when attempting to load a library from an invalid path.

runtime/vm/object.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 "vm/object.h"
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/assembler.h"
 #include "vm/become.h"
@@ skipping 10990 matching lines @@
       TransitionVMToNative transition(thread);
       Api::Scope api_scope(thread);
       obj = Api::UnwrapHandle(handler(Dart_kImportTag,
                                       Api::NewHandle(thread, importer()),
                                       Api::NewHandle(thread, lib_url.raw())));
     }
     if (obj.IsError()) {
       Exceptions::PropagateError(Error::Cast(obj));
     }
   } else {
-    // Another load request is in flight.
-    ASSERT(deferred_lib.LoadRequested());
+    // Another load request is in flight or previously failed.
+    ASSERT(deferred_lib.LoadRequested() || deferred_lib.LoadFailed());
   }
   return false;  // Load request not yet completed.
 }
 
 
 RawArray* LibraryPrefix::dependent_code() const {
   return raw_ptr()->dependent_code_;
 }
 
 
@@ skipping 11741 matching lines @@
   return UserTag::null();
 }
 
 
 const char* UserTag::ToCString() const {
   const String& tag_label = String::Handle(label());
   return tag_label.ToCString();
 }
 
 }  // namespace dart