Properly clean up notification on download open

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 4658f1de5a0d4b2a3302202a0ee2122702532f7b..58d47749dd6ff15fded94f41ce9ca3755456729f 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
@@ -796,12 +796,14 @@ public class DownloadNotificationService extends Service {
     }
 
     /**
-     * Cancel a download notification.
+     * Removes a download notification and all associated tracking.  This method relies on the
+     * caller to provide the notification id, which is useful in the case where the internal
+     * tracking doesn't exist (e.g. in the case of a successful download, where we show the download
+     * completed notification and remove our internal state tracking).
      * @param notificationId Notification ID of the download
      * @param downloadGuid GUID of the download.
      */
-    @VisibleForTesting
-    void cancelNotification(int notificationId, String downloadGuid) {
+    public void cancelNotification(int notificationId, String downloadGuid) {
         mNotificationManager.cancel(NOTIFICATION_NAMESPACE, notificationId);
         mDownloadSharedPreferenceHelper.removeSharedPreferenceEntry(downloadGuid);
 
@@ -816,7 +818,8 @@ public class DownloadNotificationService extends Service {
     }
 
     /**
-     * Called when a download is canceled.
+     * Called when a download is canceled.  This method uses internal tracking to try to find the
+     * notification id to cancel.
      * @param downloadGuid GUID of the download.
      */
     @VisibleForTesting