Add UMA for studying download cancellation reasons

chrome/browser/android/download/download_manager_service.h

Index: chrome/browser/android/download/download_manager_service.h
diff --git a/chrome/browser/android/download/download_manager_service.h b/chrome/browser/android/download/download_manager_service.h
index 695d3462ae64d776fcd66f3d29a4796a5b2a4612..22dfb3e59faabfa629b489a75507103832395643 100644
--- a/chrome/browser/android/download/download_manager_service.h
+++ b/chrome/browser/android/download/download_manager_service.h
@@ -43,7 +43,8 @@ class DownloadManagerService : public DownloadHistory::Observer {
   void CancelDownload(JNIEnv* env,
                       jobject obj,
                       const JavaParamRef<jstring>& jdownload_guid,
-                      bool is_off_the_record);
+                      bool is_off_the_record,
+                      bool is_notification_dismissed);
 
   // Called to pause a download item that has GUID equal to |jdownload_guid|.
   // If the DownloadItem is not yet created, do nothing as it is already paused.