Make the UI an observer of downloads.

android_webview/native/aw_web_contents_delegate.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "android_webview/native/aw_web_contents_delegate.h"
 
 #include "android_webview/browser/find_helper.h"
 #include "android_webview/native/aw_contents.h"
 #include "android_webview/native/aw_javascript_dialog_manager.h"
 #include "base/android/scoped_java_ref.h"
@@ skipping 43 matching lines @@
 
 bool AwWebContentsDelegate::CanDownload(content::RenderViewHost* source,
                                         int request_id,
                                         const std::string& request_method) {
   // Android webview intercepts download in its resource dispatcher host
   // delegate, so should not reach here.
   NOTREACHED();
   return false;
 }
 
-void AwWebContentsDelegate::OnStartDownload(WebContents* source,
-                                            content::DownloadItem* download) {
-  NOTREACHED();  // Downloads are cancelled in ResourceDispatcherHostDelegate.
-}
-
 void AwWebContentsDelegate::AddNewContents(content::WebContents* source,
                                            content::WebContents* new_contents,
                                            WindowOpenDisposition disposition,
                                            const gfx::Rect& initial_pos,
                                            bool user_gesture,
                                            bool* was_blocked) {
   JNIEnv* env = AttachCurrentThread();
 
   bool is_dialog = disposition == NEW_POPUP;
   ScopedJavaLocalRef<jobject> java_delegate = GetJavaDelegate(env);
@@ skipping 44 matching lines @@
   if (java_delegate.obj()) {
     Java_AwWebContentsDelegate_activateContents(env, java_delegate.obj());
   }
 }
 
 bool RegisterAwWebContentsDelegate(JNIEnv* env) {
   return RegisterNativesImpl(env);
 }
 
 }  // namespace android_webview