Use permanent Content Suggestions Server endpoint.

The only real change here is the flag. The other constants are only used
to log a warning on unrecognized endpoints. With the flag enabled on
this change, the browser will use the prod instance instead of the dev
instance. We can still set an arbitrary endpoint via adb or Finch.

Eventually, we'll have logic to switch between endpoints based on
channel. For the time being, though, we're dependent on Finch for the
server to be enabled at all, so we can handle that in Finch too.

Also eventually, we'll want a flag that just selects between endpoints,
but I'd wait until after branch point for that.

BUG=633613

Review-Url: https://codereview.chromium.org/2269963002
Cr-Commit-Position: refs/heads/master@{#413814}
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index ea18d75..8146332 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -562,12 +562,12 @@
 
 const FeatureEntry::FeatureParam kNTPSnippetsFeatureVariationServer[] = {
     {"content_suggestions_backend",
-     ntp_snippets::kContentSuggestionsSandboxServer}};
+     ntp_snippets::kContentSuggestionsServer}};
 
 const FeatureEntry::FeatureParam
     kNTPSnippetsFeatureVariationServerNonPersonalized[] = {
         {"content_suggestions_backend",
-         ntp_snippets::kContentSuggestionsSandboxServer},
+         ntp_snippets::kContentSuggestionsServer},
         {"fetching_personalization", "non_personal"}};
 
 const FeatureEntry::FeatureVariation kNTPSnippetsFeatureVariations[] = {