Local NTP: add smoke tests for doodles

Split LogoService into LogoService interface and LogoServiceImpl to make
it easier to provide fake data to the test.

Bug: 768419
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I84639189d2db1b24a2e139936c99369352bab587
Reviewed-on: https://chromium-review.googlesource.com/690198
Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Reviewed-by: Marc Treib <treib@chromium.org>
Commit-Queue: Chris Pickel <sfiera@chromium.org>
Cr-Commit-Position: refs/heads/master@{#505374}
  explicit CustomNTPUrlTest(const std::string& ntp_file_path)
      : https_test_server_(net::EmbeddedTestServer::TYPE_HTTPS),
        ntp_file_path_(ntp_file_path) {
    https_test_server_.ServeFilesFromSourceDirectory(
        "chrome/test/data/local_ntp");
  }

  explicit CustomNTPUrlTest(const std::string& ntp_file_path)
      : https_test_server_(net::EmbeddedTestServer::TYPE_HTTPS),
        ntp_file_path_(ntp_file_path) {
    https_test_server_.ServeFilesFromSourceDirectory(
        "chrome/test/data/local_ntp");
  }
