NetworkService: Destroy URLLoaders when a NetworkContext is destroyed.

content/network/network_context.h

Index: content/network/network_context.h
diff --git a/content/network/network_context.h b/content/network/network_context.h
index 51834fe5295b24ad41af5e150606cfcc99849508..a4dd42c2b6808c637e36c76dc9dc485e275ca189 100644
--- a/content/network/network_context.h
+++ b/content/network/network_context.h
@@ -62,10 +62,6 @@ class NetworkContext : public mojom::NetworkContext {
   // net::URLRequestContext (held by NetworkContext) is destroyed.
   std::set<URLLoaderImpl*> url_loaders_;
 
-  // Set when entering the destructor, in order to avoid manipulations of the
-  // |url_loaders_| (as a url_loader might delete itself in Cleanup()).
-  bool in_shutdown_;
-
   mojom::NetworkContextParamsPtr params_;
 
   mojo::Binding<mojom::NetworkContext> binding_;