DownloadsApiTest uses a ScopedTempDir to clean up after itself.

chrome/browser/extensions/extension_downloads_apitest.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/extensions/extension_apitest.h"
+#include "chrome/browser/prefs/pref_service.h"
+#include "chrome/browser/profiles/profile.h"
+#include "chrome/browser/ui/browser.h"
 #include "chrome/common/chrome_switches.h"
+#include "chrome/common/pref_names.h"
 
 class DownloadsApiTest : public ExtensionApiTest {
  public:
   void SetUpCommandLine(CommandLine* command_line) {
     ExtensionApiTest::SetUpCommandLine(command_line);
     command_line->AppendSwitch(switches::kEnableExperimentalExtensionApis);
   }
+
+  void SetUpTempDownloadsDir() {
+    ASSERT_TRUE(tmpdir.CreateUniqueTempDir());
+    browser()->profile()->GetPrefs()->SetFilePath(
+        prefs::kDownloadDefaultDirectory, tmpdir.path());
+  }
+
+ private:
+  ScopedTempDir tmpdir;
 };
 
-// Disabled: see http://crbug.com/101170
-IN_PROC_BROWSER_TEST_F(DownloadsApiTest, DISABLED_Downloads) {
+IN_PROC_BROWSER_TEST_F(DownloadsApiTest, Downloads) {
+  SetUpTempDownloadsDir();
   ASSERT_TRUE(StartTestServer());
   ASSERT_TRUE(RunExtensionTest("downloads")) << message_;
 }