Extensions installed by policy overrun previously installed extensions.

chrome/browser/extensions/pending_extension_manager.h

Index: chrome/browser/extensions/pending_extension_manager.h
diff --git a/chrome/browser/extensions/pending_extension_manager.h b/chrome/browser/extensions/pending_extension_manager.h
index 6efbdeb575d8a5704534ffb22a4af67128815476..e80392b25aa3241ed8a60a631873eb2706d2fc74 100644
--- a/chrome/browser/extensions/pending_extension_manager.h
+++ b/chrome/browser/extensions/pending_extension_manager.h
@@ -72,9 +72,12 @@ class PendingExtensionManager {
 
   // Given an extension id and an update URL, schedule the extension
   // to be fetched, installed, and activated.
+  // If |overwrite| is true, an existing extension with the same id will
+  // be replaced by the extension fetched.
   void AddFromExternalUpdateUrl(const std::string& id,
                                 const GURL& update_url,
-                                Extension::Location location);
+                                Extension::Location location,
+                                bool overwrite);
 
   // Add a pending extension record for an external CRX file.
   void AddFromExternalFile(