Supervised user blacklist: Don't download the blacklist file on every startup

BUG=410824

Review URL: https://codereview.chromium.org/1086393002

Cr-Commit-Position: refs/heads/master@{#325462}

chrome/browser/supervised_user/supervised_user_service.cc

@@ -6,10 +6,12 @@
 
 #include "base/command_line.h"
 #include "base/files/file_path.h"
+#include "base/files/file_util.h"
 #include "base/memory/ref_counted.h"
 #include "base/path_service.h"
 #include "base/prefs/pref_service.h"
 #include "base/strings/utf_string_conversions.h"
+#include "base/task_runner_util.h"
 #include "base/version.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/component_updater/supervised_user_whitelist_installer.h"
@@ -620,8 +622,18 @@ void SupervisedUserService::OnSiteListUpdated() {
 
 void SupervisedUserService::LoadBlacklist(const base::FilePath& path,
                                           const GURL& url) {
-  // TODO(treib): Don't re-download the blacklist if the local file exists!
-  if (!url.is_valid()) {
+  base::PostTaskAndReplyWithResult(
+      BrowserThread::GetBlockingPool(),
+      FROM_HERE,
+      base::Bind(&base::PathExists, path),
+      base::Bind(&SupervisedUserService::OnBlacklistFileChecked,
+                 weak_ptr_factory_.GetWeakPtr(), path, url));
+}
+
+void SupervisedUserService::OnBlacklistFileChecked(const base::FilePath& path,
+                                                   const GURL& url,
+                                                   bool file_exists) {
+  if (file_exists) {
     LoadBlacklistFromFile(path);
     return;
   }

chrome/browser/supervised_user/supervised_user_service.h

@@ -281,13 +281,17 @@ class SupervisedUserService : public KeyedService,
   void OnSiteListsChanged(
       const std::vector<scoped_refptr<SupervisedUserSiteList>>& site_lists);
 
-  // Asynchronously downloads a static blacklist file from |url|, stores it at
-  // |path|, loads it, and applies it to the URL filters. If |url| is not valid
-  // (e.g. empty), directly tries to load from |path|.
+  // Asynchronously loads a blacklist from a binary file at |path| and applies
+  // it to the URL filters. If no file exists at |path| yet, downloads a file
+  // from |url| and stores it at |path| first.
   void LoadBlacklist(const base::FilePath& path, const GURL& url);
 
-  // Asynchronously loads a static blacklist from a binary file at |path| and
-  // applies it to the URL filters.
+  void OnBlacklistFileChecked(const base::FilePath& path,
+                              const GURL& url,
+                              bool file_exists);
+
+  // Asynchronously loads a blacklist from a binary file at |path| and applies
+  // it to the URL filters.
   void LoadBlacklistFromFile(const base::FilePath& path);
 
   void OnBlacklistDownloadDone(const base::FilePath& path, bool success);