Addressing minor review comments in ExtensionProcessManager post-submit.

BUG=None
TEST=None (no significant changes)

Review URL: http://codereview.chromium.org/159073

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@21244 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/extensions/extension_process_manager.cc

@@ -90,6 +90,9 @@ void ExtensionProcessManager::RegisterExtensionProcess(
   if (it != process_ids_.end() && (*it).second == process_id)
     return;
 
+  // Extension ids should get removed from the map before the process ids get
+  // reused from a dead renderer.
+  DCHECK(it == process_ids_.end());
   process_ids_[extension_id] = process_id;
 
   ExtensionsService* extension_service =