Clear Shill stub config in offline file manager tests

The Shill stub client fakes ethernet and wifi connections during
testing. Clear its config during offline tests to simulate a lack of
network connectivity.

As a side effect, fileManagerPrivate.getDriveConnectionState will no
longer need to be stubbed out, as it will now think the device is
offline and return the appropriate result.

Bug: 925272
Change-Id: Idd6cb44325cfde4991d3b1e64185a28e8655c733
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1578149
Commit-Queue: Austin Tankiang <austinct@chromium.org>
Reviewed-by: Sam McNally <sammc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#654782}
    static void RegisterJSONConverter(
        base::JSONValueConverter<TestEntryInfo>* converter) {
      converter->RegisterCustomField("type", &TestEntryInfo::type,
                                     &MapStringToEntryType);
      converter->RegisterStringField("sourceFileName",
                                     &TestEntryInfo::source_file_name);
      converter->RegisterStringField("targetPath", &TestEntryInfo::target_path);
      converter->RegisterStringField("nameText", &TestEntryInfo::name_text);
      converter->RegisterStringField("teamDriveName",
                                     &TestEntryInfo::team_drive_name);
      converter->RegisterStringField("computerName",
                                     &TestEntryInfo::computer_name);
      converter->RegisterStringField("mimeType", &TestEntryInfo::mime_type);
      converter->RegisterCustomField("sharedOption",
                                     &TestEntryInfo::shared_option,
                                     &MapStringToSharedOption);
      converter->RegisterCustomField("lastModifiedTime",
                                     &TestEntryInfo::last_modified_time,
                                     &MapStringToTime);
      converter->RegisterNestedField("capabilities",
                                     &TestEntryInfo::capabilities);
      converter->RegisterNestedField("folderFeature",
                                     &TestEntryInfo::folder_feature);
      converter->RegisterBoolField("pinned", &TestEntryInfo::pinned);
    }

    static void RegisterJSONConverter(
        base::JSONValueConverter<TestEntryInfo>* converter) {
      converter->RegisterCustomField("type", &TestEntryInfo::type,
                                     &MapStringToEntryType);
      converter->RegisterStringField("sourceFileName",
                                     &TestEntryInfo::source_file_name);
      converter->RegisterStringField("targetPath", &TestEntryInfo::target_path);
      converter->RegisterStringField("nameText", &TestEntryInfo::name_text);
      converter->RegisterStringField("teamDriveName",
                                     &TestEntryInfo::team_drive_name);
      converter->RegisterStringField("computerName",
                                     &TestEntryInfo::computer_name);
      converter->RegisterStringField("mimeType", &TestEntryInfo::mime_type);
      converter->RegisterCustomField("sharedOption",
                                     &TestEntryInfo::shared_option,
                                     &MapStringToSharedOption);
      converter->RegisterCustomField("lastModifiedTime",
                                     &TestEntryInfo::last_modified_time,
                                     &MapStringToTime);
      converter->RegisterNestedField("capabilities",
                                     &TestEntryInfo::capabilities);
      converter->RegisterNestedField("folderFeature",
                                     &TestEntryInfo::folder_feature);
      converter->RegisterBoolField("pinned", &TestEntryInfo::pinned);
    }
