Revert "[Android O] Clean up notification settings on channel migration"

This reverts commit 7860090b.

Reason for revert: Likely cause of ANR / DCHECK

Original change's description:
> [Android O] Clean up notification settings on channel migration
> 
> - Previously when migrating to channels, the content settings were
> simply copied over to the NotificationChannelsProviderAndroid from
> the PrefProvider.
> 
> - Now they are deleted from the PrefProvider as they are copied over
> to the NCPA.
> 
> - This avoids old content settings hanging around and getting
> reinstated on channel deletion.
> 
> Bug: 781524
> Change-Id: Ic00ddd4996e8a17775678193b6ffdb0b4d62d5fa
> Reviewed-on: https://chromium-review.googlesource.com/760936
> Reviewed-by: Raymes Khoury <raymes@chromium.org>
> Reviewed-by: Peter Beverloo <peter@chromium.org>
> Commit-Queue: Anita Woodruff <awdf@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#515538}

TBR=raymes@chromium.org,peter@chromium.org,awdf@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 781524,784823
Change-Id: I53d19029118bbd0c907ad1317f744e3e6e0a80c3
Reviewed-on: https://chromium-review.googlesource.com/768787Reviewed-by: Anita Woodruff <awdf@chromium.org>
Commit-Queue: Anita Woodruff <awdf@chromium.org>
Cr-Commit-Position: refs/heads/master@{#516297}

chrome/browser/notifications/notification_channels_provider_android.cc

@@ -188,14 +188,8 @@ void NotificationChannelsProviderAndroid::MigrateToChannelsIfNecessary(
   std::unique_ptr<content_settings::RuleIterator> it(
       pref_provider->GetRuleIterator(CONTENT_SETTINGS_TYPE_NOTIFICATIONS,
                                      std::string(), false /* incognito */));
-  while (it && it->HasNext()) {
-    const content_settings::Rule& rule = it->Next();
-    CreateChannelForRule(rule);
-    pref_provider->SetWebsiteSetting(
-        rule.primary_pattern, rule.secondary_pattern,
-        CONTENT_SETTINGS_TYPE_NOTIFICATIONS,
-        content_settings::ResourceIdentifier(), nullptr);
-  }
+  while (it && it->HasNext())
+    CreateChannelForRule(it->Next());
   prefs->SetBoolean(prefs::kMigratedToSiteNotificationChannels, true);
 }
 

chrome/browser/notifications/notification_channels_provider_android_unittest.cc

@@ -602,9 +602,6 @@ TEST_F(NotificationChannelsProviderAndroidTest,
       checked_blocked = true;
     }
   }
-  EXPECT_FALSE(
-      old_provider->GetRuleIterator(CONTENT_SETTINGS_TYPE_NOTIFICATIONS,
-                                    std::string(), false /* incognito */));
 }
 
 TEST_F(NotificationChannelsProviderAndroidTest,

components/content_settings/core/test/content_settings_mock_provider.cc

@@ -28,13 +28,8 @@ bool MockProvider::SetWebsiteSetting(
     base::Value* value) {
   if (read_only_)
     return false;
-  if (value) {
-    value_map_.SetValue(requesting_url_pattern, embedding_url_pattern,
-                        content_type, resource_identifier, base::Time(), value);
-  } else {
-    value_map_.DeleteValue(requesting_url_pattern, embedding_url_pattern,
-                           content_type, resource_identifier);
-  }
+  value_map_.SetValue(requesting_url_pattern, embedding_url_pattern,
+                      content_type, resource_identifier, base::Time(), value);
   return true;
 }