Speculative fix for content_action.cc crash.

This CL changes RulesRegistry::DeserializeAndAddRules() to bail out if
the extension has been unloaded. This may have been the cause of some
crashes where a ContentAction was being created for an unloaded
extension.

Bug: 1010336, 1115969
Change-Id: Ibbd01c1b5b0a8f4cc3c2668fbb4b804189ba0b20
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2345939
Commit-Queue: calamity <calamity@chromium.org>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#800433}

extensions/browser/api/declarative/rules_registry.cc

@@ -21,6 +21,7 @@
 #include "extensions/browser/api/declarative/rules_cache_delegate.h"
 #include "extensions/browser/extension_error.h"
 #include "extensions/browser/extension_prefs.h"
+#include "extensions/browser/extension_registry.h"
 #include "extensions/browser/extension_system.h"
 #include "extensions/browser/extensions_browser_client.h"
 #include "extensions/browser/state_store.h"
@@ -311,6 +312,14 @@ void RulesRegistry::DeserializeAndAddRules(const std::string& extension_id,
                                            std::unique_ptr<base::Value> rules) {
   DCHECK_CURRENTLY_ON(owner_thread());
 
+  // Since this is called in response to asynchronously loading rules from
+  // storage, the extension may have been unloaded by the time this is called.
+  if (!ExtensionRegistry::Get(browser_context())
+           ->enabled_extensions()
+           .Contains(extension_id)) {
+    return;
+  }
+
   std::string error = AddRulesNoFill(extension_id, RulesFromValue(rules.get()),
                                      &rules_, nullptr);
   if (!error.empty())