Supervised users: Add a cmdline flag and about:flags entry to enable the host blacklist

BUG=410824

Review URL: https://codereview.chromium.org/545193003

Cr-Commit-Position: refs/heads/master@{#293740}

chrome/app/generated_resources.grd

@@ -6121,6 +6121,12 @@ Keep your key file in a safe place. You will need it to create new versions of y
       <message name="IDS_FLAGS_ENABLE_SUGGESTIONS_SERVICE_DESCRIPTION" desc="Description for the flag to enable suggestions service.">
         Enable the experimental Chrome suggestions service.
       </message>
+      <message name="IDS_FLAGS_ENABLE_SUPERVISED_USER_BLACKLIST_NAME" desc="Name of the flag to enable the supervised user host blacklist.">
+        Enable the supervised user host blacklist
+      </message>
+      <message name="IDS_FLAGS_ENABLE_SUPERVISED_USER_BLACKLIST_DESCRIPTION" desc="Description for the flag to enable the supervised user host blacklist.">
+        Enable the host blacklist for use by supervised users.
+      </message>
       <message name="IDS_FLAGS_ENABLE_SYNCED_NOTIFICATIONS_NAME" desc="Name of the flag to enable synced notifications.">
         Enable Synced Notifications
       </message>

chrome/browser/about_flags.cc

@@ -1169,6 +1169,13 @@ const Experiment kExperiments[] = {
     ENABLE_DISABLE_VALUE_TYPE(switches::kEnableSuggestionsService,
                               switches::kDisableSuggestionsService)
   },
+  {
+    "enable-supervised-user-blacklist",
+    IDS_FLAGS_ENABLE_SUPERVISED_USER_BLACKLIST_NAME,
+    IDS_FLAGS_ENABLE_SUPERVISED_USER_BLACKLIST_DESCRIPTION,
+    kOsAndroid | kOsMac | kOsWin | kOsLinux | kOsCrOS,
+    SINGLE_VALUE_TYPE(switches::kEnableSupervisedUserBlacklist)
+  },
   {
     "enable-sync-synced-notifications",
     IDS_FLAGS_ENABLE_SYNCED_NOTIFICATIONS_NAME,

chrome/browser/supervised_user/supervised_user_service.cc

@@ -715,7 +715,10 @@ void SupervisedUserService::SetActive(bool active) {
     UpdateSiteLists();
     UpdateManualHosts();
     UpdateManualURLs();
-    if (delegate_) {
+    bool use_blacklist =
+        CommandLine::ForCurrentProcess()->HasSwitch(
+            switches::kEnableSupervisedUserBlacklist);
+    if (delegate_ && use_blacklist) {
       base::FilePath blacklist_path = delegate_->GetBlacklistPath();
       if (!blacklist_path.empty())
         LoadBlacklist(blacklist_path);

chrome/common/chrome_switches.cc

@@ -604,6 +604,10 @@ const char kEnableStreamlinedHostedApps[]   = "enable-streamlined-hosted-apps";
 // Enables the suggestions service.
 const char kEnableSuggestionsService[]      = "enable-suggestions-service";
 
+// Enables the supervised user host blacklist.
+const char kEnableSupervisedUserBlacklist[] =
+    "enable-supervised-user-blacklist";
+
 // Enables synced notifications.
 const char kEnableSyncSyncedNotifications[] =
     "enable-sync-synced-notifications";

chrome/common/chrome_switches.h

@@ -174,6 +174,7 @@ extern const char kEnableSpellingFeedbackFieldTrial[];
 extern const char kEnableSSLConnectJobWaiting[];
 extern const char kEnableStreamlinedHostedApps[];
 extern const char kEnableSuggestionsService[];
+extern const char kEnableSupervisedUserBlacklist[];
 extern const char kEnableSyncArticles[];
 extern const char kEnableSyncSyncedNotifications[];
 extern const char kEnableThumbnailRetargeting[];

tools/metrics/histograms/histograms.xml

@@ -44295,6 +44295,7 @@ To add a new entry, add it with any value and run test to compute valid value.
   <int value="-1399419572" label="enable-app-list"/>
   <int value="-1392562498" label="disable-origin-chip"/>
   <int value="-1375111024" label="enable-fixed-position-compositing"/>
+  <int value="-1358669137" label="enable-supervised-user-blacklist"/>
   <int value="-1349872906"
       label="disallow-autofill-sync-credential-for-reauth"/>
   <int value="-1341092934" label="enable-accelerated-overflow-scroll"/>