Create an external source for extensions on linux that meets the needs of package managers.

chrome/browser/extensions/external_extension_provider_impl.cc

Index: chrome/browser/extensions/external_extension_provider_impl.cc
diff --git a/chrome/browser/extensions/external_extension_provider_impl.cc b/chrome/browser/extensions/external_extension_provider_impl.cc
index d9f332ea7faadfd71c9dbaf35a418545c9472e65..c4cacc300703286e9daf78d3dd9c4a5142afe75f 100644
--- a/chrome/browser/extensions/external_extension_provider_impl.cc
+++ b/chrome/browser/extensions/external_extension_provider_impl.cc
@@ -35,6 +35,10 @@
 #include "chrome/browser/extensions/default_apps.h"
 #endif
 
+#if defined(OS_LINUX) && !defined(OS_CHROMEOS)
+#include "chrome/browser/extensions/external_filesystem_extension_loader_linux.h"
+#endif
+
 #if defined(OS_WIN)
 #include "chrome/browser/extensions/external_registry_extension_loader_win.h"
 #endif
@@ -355,6 +359,19 @@ void ExternalExtensionProviderImpl::CreateExternalProviders(
               Extension::INVALID,
               Extension::NO_FLAGS)));
 #endif
+
+#if defined(OS_LINUX) && !defined(OS_CHROMEOS)
+  provider_list->push_back(
+      linked_ptr<ExternalExtensionProviderInterface>(
+          new ExternalExtensionProviderImpl(
+              service,
+              new ExternalFilesystemExtensionLoader(
+                  chrome::DIR_SINGLE_EXTERNAL_EXTENSIONS),
+              Extension::EXTERNAL_PREF,
+              Extension::EXTERNAL_PREF_DOWNLOAD,
+              Extension::NO_FLAGS)));
+#endif
+
   provider_list->push_back(
       linked_ptr<ExternalExtensionProviderInterface>(
           new ExternalExtensionProviderImpl(