Standalone embedder seems to leak libraries loaded via IsolateMirror.loadUri

[mkustermann]

The implementation of IsolateMirror.loadUri calls out to the embedder to load the library, see runtime/lib/mirrors.cc:

DEFINE_NATIVE_ENTRY(IsolateMirror_loadUri, 0, 1) {
  ...

  // Request the embedder to load the library.
  isolate->BlockClassFinalization();
  Object& result = Object::Handle(
      zone, isolate->CallTagHandler(
                Dart_kImportTag,
                Library::Handle(zone, isolate->object_store()->root_library()),
                canonical_uri));
  isolate->UnblockClassFinalization();
  ...
  if (!ClassFinalizer::ProcessPendingClasses()) {
    Exceptions::PropagateError(Error::Handle(thread->sticky_error()));
  }

Looking at the code in runtime/bin/loader.cc:

    if (dfe.CanUseDartFrontend() && dfe.UseDartFrontend() &&
        (tag == Dart_kImportTag)) {
      // E.g., IsolateMirror.loadUri.
      char* error = NULL;
      int exit_code = 0;
      uint8_t* kernel_buffer = NULL;
      intptr_t kernel_buffer_size = -1;
      dfe.CompileAndReadScript(url_string, &kernel_buffer, &kernel_buffer_size,
                               &error, &exit_code, NULL);
      if (exit_code == 0) {
        return Dart_LoadLibraryFromKernel(kernel_buffer, kernel_buffer_size);
        ...

It seems this kernel buffer is never freed and thereby leaked (process-wide, even after the isolate is shutdown).

/cc @rmacnak-google