Fix OfflinePageDownloadBridge. Calls native->Java did not work due to missed JNI initialization.

chrome/browser/android/offline_pages/downloads/offline_page_download_bridge.cc

Index: chrome/browser/android/offline_pages/downloads/offline_page_download_bridge.cc
diff --git a/chrome/browser/android/offline_pages/downloads/offline_page_download_bridge.cc b/chrome/browser/android/offline_pages/downloads/offline_page_download_bridge.cc
index 33e120ff9fa19876af4f516c62fa45930d9bd023..4ae4a7e73868987b8b638174ce16edef68be4799 100644
--- a/chrome/browser/android/offline_pages/downloads/offline_page_download_bridge.cc
+++ b/chrome/browser/android/offline_pages/downloads/offline_page_download_bridge.cc
@@ -55,7 +55,8 @@ OfflinePageDownloadBridge::OfflinePageDownloadBridge(
     JNIEnv* env,
     const JavaParamRef<jobject>& obj,
     DownloadUIAdapter* download_ui_adapter)
-    : download_ui_adapter_(download_ui_adapter) {
+    : weak_java_ref_(env, obj),
+      download_ui_adapter_(download_ui_adapter) {
   DCHECK(download_ui_adapter_);
   download_ui_adapter_->AddObserver(this);
 }