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}
void LogoService::SetClockForTests(std::unique_ptr<base::Clock> clock) {

void LogoService::SetClockForTests(std::unique_ptr<base::Clock> clock) {
  clock_for_test_ = std::move(clock);
}
