Avoid changing enabled features while the browser is already running.

chrome/test/base/in_process_browser_test.cc

Index: chrome/test/base/in_process_browser_test.cc
diff --git a/chrome/test/base/in_process_browser_test.cc b/chrome/test/base/in_process_browser_test.cc
index 8d8cac931a7f3c1e0e08a71af6cc84f7b01f7ed6..fa30cc26712920c6cc96ae2a78793d342de10a9c 100644
--- a/chrome/test/base/in_process_browser_test.cc
+++ b/chrome/test/base/in_process_browser_test.cc
@@ -191,11 +191,6 @@ void InProcessBrowserTest::SetUp() {
   // Browser tests will create their own g_browser_process later.
   DCHECK(!g_browser_process);
 
-  // Clear the FeatureList instance from base/test/test_suite.cc. Since this is
-  // a browser test, a FeatureList will be registered as part of normal browser
-  // start up in ChromeBrowserMainParts::SetupMetricsAndFieldTrials().
-  base::FeatureList::ClearInstanceForTesting();
-
   base::CommandLine* command_line = base::CommandLine::ForCurrentProcess();
 
   // Auto-reload breaks many browser tests, which assume error pages won't be