[NTP Snippets] Fetch/load snippets on startup, and pass them on NTP creation

components/ntp_snippets/ntp_snippets_service.cc

 // Copyright 2015 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_service.h"
 
 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
 #include "base/json/json_string_value_serializer.h"
 #include "base/location.h"
@@ skipping 30 matching lines @@
       snippets_fetcher_(std::move(snippets_fetcher)),
       weak_ptr_factory_(this) {
   snippets_fetcher_callback_ = snippets_fetcher_->AddCallback(
       base::Bind(&NTPSnippetsService::OnSnippetsDownloaded,
                  weak_ptr_factory_.GetWeakPtr()));
 }
 
 NTPSnippetsService::~NTPSnippetsService() {}
 
 void NTPSnippetsService::Init(bool enabled) {
+  // If enabled, get snippets immediately. If we've downloaded them before,
+  // this will just read from disk.
+  if (enabled)
+    FetchSnippets(false);
+
   // The scheduler only exists on Android so far, it's null on other platforms.
   if (!scheduler_)
     return;
 
   if (enabled)
     scheduler_->Schedule(kDefaultFetchingIntervalSeconds);
   else
     scheduler_->Unschedule();
 }
 
@@ skipping 19 matching lines @@
 
 void NTPSnippetsService::OnFileReadDone(const std::string* json, bool success) {
   if (!success)
     return;
 
   DCHECK(json);
   LoadFromJSONString(*json);
 }
 
 bool NTPSnippetsService::LoadFromJSONString(const std::string& str) {
+  snippets_.clear();
+
   JSONStringValueDeserializer deserializer(str);
   int error_code;
   std::string error_message;
 
   scoped_ptr<base::Value> deserialized =
       deserializer.Deserialize(&error_code, &error_message);
   if (!deserialized)
     return false;
 
   const base::DictionaryValue* top_dict = NULL;
@@ skipping 29 matching lines @@
     const base::FilePath& download_path) {
   std::string* downloaded_data = new std::string;
   base::PostTaskAndReplyWithResult(
       file_task_runner_.get(), FROM_HERE,
       base::Bind(&ReadFileToString, download_path, downloaded_data),
       base::Bind(&NTPSnippetsService::OnFileReadDone,
                  weak_ptr_factory_.GetWeakPtr(), base::Owned(downloaded_data)));
 }
 
 }  // namespace ntp_snippets