Move small c/b/extensions classes into extensions namespace no.2

chrome/browser/extensions/platform_app_browsertest_util.cc

Index: chrome/browser/extensions/platform_app_browsertest_util.cc
diff --git a/chrome/browser/extensions/platform_app_browsertest_util.cc b/chrome/browser/extensions/platform_app_browsertest_util.cc
index c108028a80e35a77b9e63673b7ba5a989818c2db..71c308026a3f61643752183c8334896cf8e5e6cb 100644
--- a/chrome/browser/extensions/platform_app_browsertest_util.cc
+++ b/chrome/browser/extensions/platform_app_browsertest_util.cc
@@ -17,12 +17,12 @@
 #include "content/public/test/test_utils.h"
 
 using content::WebContents;
-using extensions::Extension;
 
 namespace utils = extension_function_test_utils;
 
-void PlatformAppBrowserTest::SetUpCommandLine(
-    CommandLine* command_line) {
+namespace extensions {
+
+void PlatformAppBrowserTest::SetUpCommandLine(CommandLine* command_line) {
   ExtensionBrowserTest::SetUpCommandLine(command_line);
   command_line->AppendSwitch(switches::kEnableExperimentalExtensionApis);
 }
@@ -119,3 +119,5 @@ void PlatformAppBrowserTest::CloseShellWindow(ShellWindow* window) {
   window->Close();
   destroyed_observer.Wait();
 }
+
+}  // namespace extensions