Bug 1399646: Part 4 - Increase the extension shutdown blocker timeout. r=mixedpuppy

The current timeout was added to deal with some shutdown deadlocks that were
happining in the wild, but were hard to reproduce locally and therefore
diagnose. It's not clear whether the bulk of those have been fixed, so I'm
reluctant to remove the timeout entirely.

But the current 1s timeout is quite short, and doesn't allow for proper
cleanup in a lot of legitimate cases. The async shutdown service starts to
emit warnings at 10s, so 8s gives us enough time to avoid at least that.

MozReview-Commit-ID: 94zZjYUY8qZ

--HG--
extra : rebase_source : 980cce2af1117d6d46f6083910672e3ef8702981
extra : histedit_source : d8d9b2d7f6312b5d8801e4e26d2b0c0a32a538c2

toolkit/components/extensions/Extension.jsm

@@ -102,7 +102,7 @@ XPCOMUtils.defineLazyGetter(this, "console", ExtensionUtils.getConsole);
 XPCOMUtils.defineLazyGetter(this, "LocaleData", () => ExtensionCommon.LocaleData);
 
 // The maximum time to wait for extension shutdown blockers to complete.
-const SHUTDOWN_BLOCKER_MAX_MS = 1000;
+const SHUTDOWN_BLOCKER_MAX_MS = 8000;
 
 // The list of properties that themes are allowed to contain.
 XPCOMUtils.defineLazyGetter(this, "allowedThemeProperties", () => {