Add request throttler to thumbnail fetching for articles on mobile NTP

components/ntp_snippets/ntp_snippets_service.h

Index: components/ntp_snippets/ntp_snippets_service.h
diff --git a/components/ntp_snippets/ntp_snippets_service.h b/components/ntp_snippets/ntp_snippets_service.h
index de27dacdae614e0528620c4487b5e2b37f2a2cb8..72c866dd2ec1f556fd419689f01fb62a38394e79 100644
--- a/components/ntp_snippets/ntp_snippets_service.h
+++ b/components/ntp_snippets/ntp_snippets_service.h
@@ -26,6 +26,7 @@
 #include "components/ntp_snippets/ntp_snippets_fetcher.h"
 #include "components/ntp_snippets/ntp_snippets_scheduler.h"
 #include "components/ntp_snippets/ntp_snippets_status_service.h"
+#include "components/ntp_snippets/request_throttler.h"
 #include "components/suggestions/suggestions_service.h"
 #include "components/sync_driver/sync_service_observer.h"
 
@@ -97,17 +98,17 @@ class NTPSnippetsService : public image_fetcher::ImageFetcherDelegate,
   bool initialized() const { return ready() || state_ == State::DISABLED; }
 
   // Fetches snippets from the server and adds them to the current ones.
-  // Requests can be marked more important by setting |force_request| to true
-  // (such request might circumvent the daily quota for requests, etc.) Useful
-  // for requests triggered by the user.
-  void FetchSnippets(bool force_request);
+  // Requests can be marked more important by setting |interactive_request| to
+  // true (such request might circumvent the daily quota for requests, etc.)
+  // Useful for requests triggered by the user.
+  void FetchSnippets(bool interactive_request);
 
   // Fetches snippets from the server for specified hosts (overriding
   // suggestions from the suggestion service) and adds them to the current ones.
   // Only called from chrome://snippets-internals, DO NOT USE otherwise!
   // Ignored while |loaded()| is false.
   void FetchSnippetsFromHosts(const std::set<std::string>& hosts,
-                              bool force_request);
+                              bool interactive_request);
 
   // Available snippets.
   const NTPSnippet::PtrVector& snippets() const { return snippets_; }
@@ -307,6 +308,9 @@ class NTPSnippetsService : public image_fetcher::ImageFetcherDelegate,
 
   const Category provided_category_;
 
+  // Request throttler for limiting requests to thumbnail images.
+  RequestThrottler thumbnail_requests_throttler_;
+
   DISALLOW_COPY_AND_ASSIGN(NTPSnippetsService);
 };