Fixed crash when chrome.runtime.reload() is called with app windows open

apps/app_window_contents.cc

Index: apps/app_window_contents.cc
diff --git a/apps/app_window_contents.cc b/apps/app_window_contents.cc
index d163c2ce84ace7bce1cdb270d9412ce4e87b2d98..7b88e67e6f6092e9d2b338d4f6be393fd1fa8ec5 100644
--- a/apps/app_window_contents.cc
+++ b/apps/app_window_contents.cc
@@ -96,7 +96,7 @@ void AppWindowContents::NativeWindowChanged(
 
   content::RenderViewHost* rvh = web_contents_->GetRenderViewHost();
   rvh->Send(new ExtensionMsg_MessageInvoke(rvh->GetRoutingID(),
-                                           host_->extension()->id(),
+                                           host_->extension_id(),

[benwells, 2013/09/20 07:35:31]

huh, I was just looking at this today due to
https://code.google.com/p/chromium/issues/detail?id=265922.

TBH I don't like the way there is extension_id, which is to be used when
extension is NULL. Feels dodgy.

[tmdiep, 2013/09/20 11:07:36]

Darn, if I had waited a bit longer this could have been fixed for me :)

If the ShellWindow sets the extension pointer to NULL when the extension
unloads, perhaps we can check and not forward the message to the render view if
it is not necessary to, since the window is closing.

                                            "app.window",
                                            "updateAppWindowProperties",
                                            args,