Add LoadState reporting to the mojo proxy resolver.

net/interfaces/proxy_resolver_service.mojom

Index: net/interfaces/proxy_resolver_service.mojom
diff --git a/net/interfaces/proxy_resolver_service.mojom b/net/interfaces/proxy_resolver_service.mojom
index abe263bb116f4f302d206bbc6f5bff655cade403..d8fd5994be5eed3527b3ca90ef96f93c0ee21d03 100644
--- a/net/interfaces/proxy_resolver_service.mojom
+++ b/net/interfaces/proxy_resolver_service.mojom
@@ -41,6 +41,7 @@ interface ProxyResolver {
 
 interface ProxyResolverRequestClient {
   ReportResult(int32 error, array<ProxyServer>? proxy_servers);
+  LoadStateChanged(int32 load_state);

[darin (slow to review), 2015/03/10 03:41:52]

note: this looks like something that would be a good fit for the
GetNextLoadState pattern. I could imagine ProxyResolver looking like this
instead:

interface ProxyResolver {
  ...

  GetProxyForURL(string url) => (int32 error, array<..>? proxy_servers);

  GetNextLoadState() => (int32 load_state);
};

This way there is no client interface. The interface is a bit simpler. You can
implement throttling for GetNextLoadState by delaying the callback.

[Sam McNally, 2015/03/10 04:00:58]

We use a client interface so the client can cancel the request by closing its
end of the pipe. Also, the load state is per-request so we'd still need an extra
pipe to identify the associated request.

[darin (slow to review), 2015/03/10 04:10:32]

Oh, I see. Silly me for not reading the comment above the GetProxyForUrl method
declaration :-/

 };
 
 interface ProxyResolverFactory {