Reland of Fix event page process cleanup when running in --isolate-extensions mode.

extensions/browser/process_manager.h

Index: extensions/browser/process_manager.h
diff --git a/extensions/browser/process_manager.h b/extensions/browser/process_manager.h
index 65ee76f8a1d2ccfda3c83d1f336cd8551aed3a15..43b766c23e9067cfc925573dc3e8daefcf905473 100644
--- a/extensions/browser/process_manager.h
+++ b/extensions/browser/process_manager.h
@@ -326,7 +326,7 @@
   // extension URLRequest is constructed and then destroyed without ever
   // starting, we can receive a completion notification without a corresponding
   // start notification. In that case we want to avoid decrementing keepalive.
-  std::set<int> pending_network_requests_;
+  std::map<int, ExtensionHost*> pending_network_requests_;
 
   // Must be last member, see doc on WeakPtrFactory.
   base::WeakPtrFactory<ProcessManager> weak_ptr_factory_;