Inject API key directly into snippets fetcher.

components/ntp_snippets/ntp_snippets_fetcher.h

Index: components/ntp_snippets/ntp_snippets_fetcher.h
diff --git a/components/ntp_snippets/ntp_snippets_fetcher.h b/components/ntp_snippets/ntp_snippets_fetcher.h
index f0800cd5699b5550f56d5533cf03c9fbe18fc545..a5d9ba3df40d5043072da7dd8c65f2c7c46dcd09 100644
--- a/components/ntp_snippets/ntp_snippets_fetcher.h
+++ b/components/ntp_snippets/ntp_snippets_fetcher.h
@@ -84,7 +84,7 @@ class NTPSnippetsFetcher : public OAuth2TokenService::Consumer,
       PrefService* pref_service,
       CategoryFactory* category_factory,
       const ParseJSONCallback& parse_json_callback,
-      bool is_stable_channel);
+      const std::string& api_key);
   ~NTPSnippetsFetcher() override;
 
   // Set a callback that is called when a new set of snippets are downloaded,
@@ -231,8 +231,8 @@ class NTPSnippetsFetcher : public OAuth2TokenService::Consumer,
   // The callback to notify when new snippets get fetched.
   SnippetsAvailableCallback snippets_available_callback_;
 
-  // Flag for picking the right (stable/non-stable) API key for Chrome Reader.
-  bool is_stable_channel_;
+  // API key to use for non-authenticated requests.
+  const std::string api_key_;
 
   // The variant of the fetching to use, loaded from variation parameters.
   Personalization personalization_;