avoid dereferencing NULL extension in ExtensionHost

chrome/browser/extensions/extension_process_manager.cc

Index: chrome/browser/extensions/extension_process_manager.cc
diff --git a/chrome/browser/extensions/extension_process_manager.cc b/chrome/browser/extensions/extension_process_manager.cc
index f21c4f8e0203fba5b9eb0fa1a41542cfdd2a6c64..23a9dc9cb6ea9a3e4073b3aa28a03873e984ef18 100644
--- a/chrome/browser/extensions/extension_process_manager.cc
+++ b/chrome/browser/extensions/extension_process_manager.cc
@@ -291,7 +291,8 @@ void ExtensionProcessManager::Observe(NotificationType type,
       for (ExtensionHostSet::iterator iter = background_hosts_.begin();
            iter != background_hosts_.end(); ++iter) {
         ExtensionHost* host = *iter;
-        if (host->extension()->id() == extension->id()) {
+        if (host->extension() == NULL ||

[Matt Perry, 2011/05/05 17:17:59]

This seems a little dangerous to me. Here's an alternative approach:
1. remove this change.
2. change ExtensionHost to hold a scoped_refptr<const Extension> rather than a
raw ptr.
3. change ExtensionHost so that it doesn't NULL out its extension_ ptr in
EXTENSION_UNLOADED. (Extension objects were not refcounted when that was
written, so it was not possible then.)
4. have ExtensionHost set a flag when it receives EXTENSION_UNLOADED, and check
that flag in places where we currently NULL-check the extension ptr.

+            host->extension()->id() == extension->id()) {
           delete host;
           // |host| should deregister itself from our structures.
           DCHECK(background_hosts_.find(host) == background_hosts_.end());