Enable extensions by default.

chrome/browser/extensions/extension_startup_unittest.cc

 #include <vector>
 
 #include "base/command_line.h"
 #include "base/file_path.h"
 #include "base/file_util.h"
 #include "base/path_service.h"
 #include "chrome/browser/browser.h"
 #include "chrome/browser/extensions/extensions_service.h"
 #include "chrome/browser/profile.h"
 #include "chrome/browser/tab_contents/tab_contents.h"
@@ skipping 27 matching lines @@
     FilePath profile_dir;
     PathService::Get(chrome::DIR_USER_DATA, &profile_dir);
     profile_dir = profile_dir.AppendASCII("Default");
     file_util::CreateDirectory(profile_dir);
 
     preferences_file_ = profile_dir.AppendASCII("Preferences");
     user_scripts_dir_ = profile_dir.AppendASCII("User Scripts");
     extensions_dir_ = profile_dir.AppendASCII("Extensions");
 
     if (enable_extensions_) {
-      command_line->AppendSwitch(switches::kEnableExtensions);
-
       FilePath src_dir;
       PathService::Get(chrome::DIR_TEST_DATA, &src_dir);
       src_dir = src_dir.AppendASCII("extensions").AppendASCII("good");
 
       file_util::CopyFile(src_dir.AppendASCII("Preferences"),
                           preferences_file_);
       file_util::CopyDirectory(src_dir.AppendASCII("Extensions"),
                                profile_dir, true);  // recursive
+    } else {
+      command_line->AppendSwitch(switches::kDisableExtensions);
     }
 
     if (enable_user_scripts_) {
       command_line->AppendSwitch(switches::kEnableUserScripts);
 
       FilePath src_dir;
       PathService::Get(chrome::DIR_TEST_DATA, &src_dir);
       src_dir = src_dir.AppendASCII("extensions").AppendASCII("good")
                        .AppendASCII("Extensions")
                        .AppendASCII("behllobkkfkfnphdnhnkndlbkcpglgmj")
@@ skipping 156 matching lines @@
 
   ui_test_utils::NavigateToURL(browser(), GURL("chrome://newtab"));
 
   bool result = false;
   ui_test_utils::ExecuteJavaScriptAndExtractBool(
       browser()->GetSelectedTabContents()->render_view_host(), L"",
       L"window.domAutomationController.send(document.title == 'Modified')",
       &result);
   EXPECT_FALSE(result);
 }