[previews component] Initialize bool fields

Previews logger was using some uninitialized bools. They are trivially
initialized in the class, so this CL makes it so.

Change-Id: I83ec951df6d79748fc538ba7cbae0018546bbe52
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1699591Reviewed-by: Tarun Bansal <tbansal@chromium.org>
Commit-Queue: Kevin Bailey <krb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#676978}

components/previews/core/previews_logger.h

@@ -123,11 +123,11 @@ class PreviewsLogger {
   std::unordered_map<std::string, base::Time> blacklisted_hosts_;
 
   // The current user blacklisted status.
-  bool user_blacklisted_status_;
+  bool user_blacklisted_status_ = false;
 
   // The current status of whether PreviewsBlackList decisions are ignored or
   // not.
-  bool blacklist_ignored_;
+  bool blacklist_ignored_ = false;
 
   // Collection of recorded navigation log messages.
   std::list<MessageLog> navigations_logs_;