Don't initialize external extensions providers if extensions are disabled

BUG=chromium-os:12709
TEST=manual, see chrome:extensions in Guest mode

Review URL: http://codereview.chromium.org/6611016

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@77455 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/chrome/browser/extensions/extension_service.cc b/chrome/browser/extensions/extension_service.cc
index dcf15d8..159785ba 100644
--- a/chrome/browser/extensions/extension_service.cc
+++ b/chrome/browser/extensions/extension_service.cc
@@ -400,8 +400,10 @@
 
   backend_ = new ExtensionServiceBackend(install_directory_);
 
-  ExternalExtensionProviderImpl::CreateExternalProviders(
-      this, profile_, &external_extension_providers_);
+  if (extensions_enabled()) {
+    ExternalExtensionProviderImpl::CreateExternalProviders(
+        this, profile_, &external_extension_providers_);
+  }
 
   // Use monochrome icons for Omnibox icons.
   omnibox_popup_icon_manager_.set_monochrome(true);