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

chrome/chrome_browser_extensions.gypi

Index: chrome/chrome_browser_extensions.gypi
diff --git a/chrome/chrome_browser_extensions.gypi b/chrome/chrome_browser_extensions.gypi
index 672a88bbf546ba4ce5723836b9972c24c08a7542..dc27f0036e08762f0b094a57b4b6f58dacfb9b4b 100644
--- a/chrome/chrome_browser_extensions.gypi
+++ b/chrome/chrome_browser_extensions.gypi
@@ -356,6 +356,10 @@
         'browser/extensions/external_extension_provider_impl.cc',
         'browser/extensions/external_extension_provider_impl.h',
         'browser/extensions/external_extension_provider_interface.h',
+        'browser/extensions/external_extension_util.cc',
+        'browser/extensions/external_extension_util.h',
+        'browser/extensions/external_filesystem_extension_loader_linux.cc',
+        'browser/extensions/external_filesystem_extension_loader_linux.h',
         'browser/extensions/external_policy_extension_loader.cc',
         'browser/extensions/external_policy_extension_loader.h',
         'browser/extensions/external_pref_extension_loader.cc',