[NTP Snippets] Fetcher: only download snippets that have a thumbnail

components/ntp_snippets/ntp_snippets_fetcher.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/ntp_snippets/ntp_snippets_fetcher.h"
 
 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
 #include "base/path_service.h"
 #include "base/strings/string_util.h"
@@ skipping 16 matching lines @@
 const char kContentSnippetsServerFormat[] =
     "https://chromereader-pa.googleapis.com/v1/fetch?key=%s";
 
 const char kRequestParameterFormat[] =
     "{"
     "  \"response_detail_level\": \"STANDARD\","
     "  \"advanced_options\": {"
     "    \"local_scoring_params\": {"
     "      \"content_params\": {"
     "        \"only_return_personalized_results\": false"
+    "      },"
+    "      \"content_restricts\": {"
+    "        \"type\": \"METADATA\","
+    "        \"value\": \"TITLE\""
+    "      },"
+    "      \"content_restricts\": {"
+    "        \"type\": \"METADATA\","
+    "        \"value\": \"SNIPPET\""
+    "      },"
+    "      \"content_restricts\": {"
+    "        \"type\": \"METADATA\","
+    "        \"value\": \"THUMBNAIL\""
     "      }"
     "%s"
     "    },"
     "    \"global_scoring_params\": {"
     "      \"num_to_return\": 10"
     "    }"
     "  }"
     "}";
 
 const char kHostRestrictFormat[] =
@@ skipping 67 matching lines @@
   }
 
   std::string response;
   bool stores_result_to_string = source->GetResponseAsString(&response);
   DCHECK(stores_result_to_string);
 
   callback_list_.Notify(response);
 }
 
 }  // namespace ntp_snippets