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

components/ntp_snippets/ntp_snippets_service.cc

Index: components/ntp_snippets/ntp_snippets_service.cc
diff --git a/components/ntp_snippets/ntp_snippets_service.cc b/components/ntp_snippets/ntp_snippets_service.cc
index 98e823d23ea5ed77a8592cd06e94c30a81bd6129..b68911ba00c03953b23eaf1678019165eedca1fa 100644
--- a/components/ntp_snippets/ntp_snippets_service.cc
+++ b/components/ntp_snippets/ntp_snippets_service.cc
@@ -49,6 +49,11 @@ NTPSnippetsService::NTPSnippetsService(
 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;
@@ -84,6 +89,8 @@ void NTPSnippetsService::OnFileReadDone(const std::string& json) {
 }
 
 bool NTPSnippetsService::LoadFromJSONString(const std::string& str) {
+  snippets_.clear();
+
   JSONStringValueDeserializer deserializer(str);
   int error_code;
   std::string error_message;