Fix crash by preventing extensions from changing their IDs.

chrome/browser/extensions/extension_service.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/extensions/extension_service.h"
 
 #include <algorithm>
 #include <set>
 
 #include "base/basictypes.h"
@@ skipping 1410 matching lines @@
     extension = Extension::Create(
         info.extension_path,
         info.extension_location,
         *info.extension_manifest,
         flags,
         &error);
   } else {
     error = errors::kManifestUnreadable;
   }
 
+  // Once installed, non-unpacked extensions cannot change their IDs (e.g., by
+  // updating the 'key' field in their manifest).
+  if (extension &&
+      extension->location() != Extension::LOAD &&
+      info.extension_id != extension->id()) {
+    error = errors::kCannotChangeExtensionID;
+    extension = NULL;

[asargent_no_longer_on_chrome, 2011/09/26 22:08:04]

It might be good to include a uma histogram here, so you could measure if this
is ever actually happening in the field. 

[jstritar, 2011/09/26 22:11:03]

Agreed. Do you think we should add a one off histogram here or collect a
histogram for extension load errors more generally in another CL?

+  }
+
   if (!extension) {
     ReportExtensionLoadError(info.extension_path,
                              error,
                              chrome::NOTIFICATION_EXTENSION_INSTALL_ERROR,
                              false);
     return;
   }
 
   if (write_to_prefs)
     extension_prefs_->UpdateManifest(extension);
@@ skipping 1450 matching lines @@
 
 ExtensionService::NaClModuleInfoList::iterator
     ExtensionService::FindNaClModule(const GURL& url) {
   for (NaClModuleInfoList::iterator iter = nacl_module_list_.begin();
        iter != nacl_module_list_.end(); ++iter) {
     if (iter->url == url)
       return iter;
   }
   return nacl_module_list_.end();
 }