Make the UI an observer of downloads.

chrome/browser/android/chrome_web_contents_delegate_android.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 "chrome/browser/android/chrome_web_contents_delegate_android.h"
 
 #include "base/android/jni_android.h"
 #include "base/metrics/histogram.h"
 #include "base/string_util.h"
 #include "chrome/browser/file_select_helper.h"
@@ skipping 258 matching lines @@
 
 bool ChromeWebContentsDelegateAndroid::CanDownload(
     content::RenderViewHost* source,
     int request_id,
     const std::string& request_method) {
   if (request_method == net::HttpRequestHeaders::kGetMethod) {
     content::DownloadControllerAndroid::Get()->CreateGETDownload(
         source, request_id);
     return false;
   }
+  // DownloadControllerAndroid::OnPostDownloadStarted() is called for the
+  // started download by the default DownloadUIController::Delegate
+  // implementation.
   return true;
 }
 
-void ChromeWebContentsDelegateAndroid::OnStartDownload(
-    WebContents* source,
-    content::DownloadItem* download) {
-  content::DownloadControllerAndroid::Get()->OnPostDownloadStarted(
-      source, download);
-}
-
 void ChromeWebContentsDelegateAndroid::DidNavigateToPendingEntry(
     content::WebContents* source) {
   navigation_start_time_ = base::TimeTicks::Now();
 }
 
 void ChromeWebContentsDelegateAndroid::DidNavigateMainFramePostCommit(
     content::WebContents* source) {
   if (!IsActiveNavigationGoogleSearch(source))
     return;
 
@@ skipping 22 matching lines @@
         web_contents, url, plugin_path, callback);
     return true;
 #else
     return false;
 #endif
 }
 
 
 }  // namespace android
 }  // namespace chrome