Don't send the service worker startup hint if suggestions are disabled.

This is controlled by the "Use a prediction service to help complete
searches and URLs typed in the address bar" setting at
chrome://settings/privacy.

Bug: 751813
Change-Id: Iedf25fbb95e4fe1133fa994843068b26b749e36b
Reviewed-on: https://chromium-review.googlesource.com/598933Reviewed-by: Mark Pearson <mpearson@chromium.org>
Commit-Queue: Justin Donnelly <jdonnelly@chromium.org>
Cr-Commit-Position: refs/heads/master@{#491740}

chrome/browser/autocomplete/chrome_autocomplete_provider_client.cc

@@ -306,6 +306,9 @@ void ChromeAutocompleteProviderClient::StartServiceWorker(
   if (!context)
     return;
 
+  if (!SearchSuggestEnabled())
+    return;
+
   context->StartServiceWorkerForNavigationHint(destination_url,
                                                base::Bind(&NoopCallback));
 }