Factor out dependncy on download throttling from core download code.

chrome/browser/download/download_request_limiter_observer.cc

+// Copyright (c) 2011 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/download/download_request_limiter_observer.h"
+
+#include "chrome/browser/browser_process.h"
+#include "chrome/browser/download/download_request_limiter.h"
+
+DownloadRequestLimiterObserver::DownloadRequestLimiterObserver(
+    TabContents* tab_contents)
+    : TabContentsObserver(tab_contents) {
+}
+
+DownloadRequestLimiterObserver::~DownloadRequestLimiterObserver() {
+}
+
+void DownloadRequestLimiterObserver::DidGetUserGesture() {
+  if (!g_browser_process->download_request_limiter())
+    return;  // NULL in unitests.
+  g_browser_process->download_request_limiter()->OnUserGesture(tab_contents());
+}