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}
content::RenderFrameHost* GetMostVisitedIframe(content::WebContents* tab) {
  CHECK_EQ(2u, tab->GetAllFrames().size());
  for (content::RenderFrameHost* frame : tab->GetAllFrames()) {
    if (frame != tab->GetMainFrame()) {
      return frame;
    }
  }
  NOTREACHED();
  return nullptr;
}

content::RenderFrameHost* GetMostVisitedIframe(content::WebContents* tab) {
  CHECK_EQ(2u, tab->GetAllFrames().size());
  for (content::RenderFrameHost* frame : tab->GetAllFrames()) {
    if (frame != tab->GetMainFrame()) {
      return frame;
    }
  }
  NOTREACHED();
  return nullptr;
}
