Set the Feature's ChannelForTesting to Trunk during extension tests, so that

chrome/browser/extensions/extension_browsertest.cc

Index: chrome/browser/extensions/extension_browsertest.cc
diff --git a/chrome/browser/extensions/extension_browsertest.cc b/chrome/browser/extensions/extension_browsertest.cc
index c0e94229406df529994fe6eeee8305b7e8f1c5e9..aefe037b269074998e289cd004baf32f4d640d10 100644
--- a/chrome/browser/extensions/extension_browsertest.cc
+++ b/chrome/browser/extensions/extension_browsertest.cc
@@ -29,6 +29,7 @@
 #include "chrome/common/chrome_notification_types.h"
 #include "chrome/common/chrome_paths.h"
 #include "chrome/common/chrome_switches.h"
+#include "chrome/common/extensions/features/feature.h"
 #include "chrome/test/base/ui_test_utils.h"
 #include "content/public/browser/navigation_controller.h"
 #include "content/public/browser/navigation_entry.h"
@@ -57,6 +58,9 @@ void ExtensionBrowserTest::SetUpCommandLine(CommandLine* command_line) {
   // This enables DOM automation for tab contentses.
   EnableDOMAutomation();
 
+  extensions::Feature::SetChannelForTesting(
+      chrome::VersionInfo::CHANNEL_UNKNOWN);
+
   PathService::Get(chrome::DIR_TEST_DATA, &test_data_dir_);
   test_data_dir_ = test_data_dir_.AppendASCII("extensions");