[Android O] Refactor channel initialization

chrome/android/java/src/org/chromium/chrome/browser/download/DownloadNotificationService.java

Index: chrome/android/java/src/org/chromium/chrome/browser/download/DownloadNotificationService.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/download/DownloadNotificationService.java b/chrome/android/java/src/org/chromium/chrome/browser/download/DownloadNotificationService.java
index 095e521f848c3071eb0d7c7389dbdfb92bf1dea2..129aaf5814c8266710acd0f2898a98bb4885a24a 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/download/DownloadNotificationService.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/download/DownloadNotificationService.java
@@ -46,6 +46,7 @@ import org.chromium.chrome.browser.download.items.OfflineContentAggregatorNotifi
 import org.chromium.chrome.browser.init.BrowserParts;
 import org.chromium.chrome.browser.init.ChromeBrowserInitializer;
 import org.chromium.chrome.browser.init.EmptyBrowserParts;
+import org.chromium.chrome.browser.notifications.ChannelsInitializer;
 import org.chromium.chrome.browser.notifications.ChromeNotificationBuilder;
 import org.chromium.chrome.browser.notifications.NotificationBuilderFactory;
 import org.chromium.chrome.browser.notifications.NotificationConstants;
@@ -366,11 +367,8 @@ public class DownloadNotificationService extends Service {
     private static Notification buildSummaryNotificationWithIcon(Context context, int iconId) {
         ChromeNotificationBuilder builder =
                 NotificationBuilderFactory
-                        .createChromeNotificationBuilder(true /* preferCompat */,
-                                NotificationConstants.CHANNEL_ID_BROWSER,
-                                context.getString(R.string.notification_category_browser),
-                                NotificationConstants.CHANNEL_GROUP_ID_GENERAL,
-                                context.getString(R.string.notification_category_group_general))
+                        .createChromeNotificationBuilder(
+                                true /* preferCompat */, ChannelsInitializer.CHANNEL_ID_BROWSER)
                         .setContentTitle(
                                 context.getString(R.string.download_notification_summary_title))
                         .setSubText(context.getString(R.string.menu_downloads))
@@ -1080,11 +1078,8 @@ public class DownloadNotificationService extends Service {
 
         ChromeNotificationBuilder builder =
                 NotificationBuilderFactory
-                        .createChromeNotificationBuilder(true /* preferCompat */,
-                                NotificationConstants.CHANNEL_ID_BROWSER,
-                                mContext.getString(R.string.notification_category_browser),
-                                NotificationConstants.CHANNEL_GROUP_ID_GENERAL,
-                                mContext.getString(R.string.notification_category_group_general))
+                        .createChromeNotificationBuilder(
+                                true /* preferCompat */, ChannelsInitializer.CHANNEL_ID_BROWSER)
                         .setContentTitle(
                                 DownloadUtils.getAbbreviatedFileName(title, MAX_FILE_NAME_LENGTH))
                         .setSmallIcon(iconId)