struct UnloadedExtensionInfo -> enum UnloadedExtensionInfoReason

We don't need to keep struct UnloadedExtensionInfo.
So removing it and use enum UnloadedExtensionInfoReason instead.

TEST=Everything runs smoothly
BUG=715144

Review-Url: https://codereview.chromium.org/2839373003
Cr-Commit-Position: refs/heads/master@{#469065}
diff --git a/extensions/browser/extension_registry.h b/extensions/browser/extension_registry.h
index 1100007..81bb6f5 100644
--- a/extensions/browser/extension_registry.h
+++ b/extensions/browser/extension_registry.h
@@ -98,7 +98,7 @@
   // Invokes the observer method OnExtensionUnloaded(). The extension must not
   // be enabled at the time of the call.
   void TriggerOnUnloaded(const Extension* extension,
-                         UnloadedExtensionInfo::Reason reason);
+                         UnloadedExtensionReason reason);
 
   // If this is a fresh install then |is_update| is false and there must not be
   // any installed extension with |extension|'s ID. If this is an update then