Use a scoped temp dir for page load metrics download test

chrome/browser/page_load_metrics/page_load_metrics_browsertest.cc

Index: chrome/browser/page_load_metrics/page_load_metrics_browsertest.cc
diff --git a/chrome/browser/page_load_metrics/page_load_metrics_browsertest.cc b/chrome/browser/page_load_metrics/page_load_metrics_browsertest.cc
index ab3266c19a2d20f5bd58511a3971787c31267095..48b7d03b985ae0489867021810d415e613ead2b2 100644
--- a/chrome/browser/page_load_metrics/page_load_metrics_browsertest.cc
+++ b/chrome/browser/page_load_metrics/page_load_metrics_browsertest.cc
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#include "base/files/scoped_temp_dir.h"
 #include "base/macros.h"
 #include "base/test/histogram_tester.h"
 #include "base/time/time.h"
@@ -16,9 +17,11 @@
 #include "chrome/browser/ui/browser.h"
 #include "chrome/browser/ui/browser_navigator_params.h"
 #include "chrome/browser/ui/tabs/tab_strip_model.h"
+#include "chrome/common/pref_names.h"
 #include "chrome/common/url_constants.h"
 #include "chrome/test/base/in_process_browser_test.h"
 #include "chrome/test/base/ui_test_utils.h"
+#include "components/prefs/pref_service.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/test/browser_test_utils.h"
 #include "content/public/test/download_test_observer.h"
@@ -173,6 +176,10 @@ IN_PROC_BROWSER_TEST_F(PageLoadMetricsBrowserTest, Ignore204Pages) {
 IN_PROC_BROWSER_TEST_F(PageLoadMetricsBrowserTest, IgnoreDownloads) {
   ASSERT_TRUE(embedded_test_server()->Start());
 
+  base::ScopedTempDir downloads_directory;
+  ASSERT_TRUE(downloads_directory.CreateUniqueTempDir());
+  browser()->profile()->GetPrefs()->SetFilePath(
+      prefs::kDownloadDefaultDirectory, downloads_directory.GetPath());
   content::DownloadTestObserverTerminal downloads_observer(
       content::BrowserContext::GetDownloadManager(browser()->profile()),
       1,  // == wait_count (only waiting for "download-test3.gif").