Implement utility-side proxy resolver factory Mojo service.

net/BUILD.gn

Index: net/BUILD.gn
diff --git a/net/BUILD.gn b/net/BUILD.gn
index da4cf9bbe6372d57592d18864fa7f40b0537c818..7f2cf97d7a75f0e6ffaedd9c78352c43929e634f 100644
--- a/net/BUILD.gn
+++ b/net/BUILD.gn
@@ -824,6 +824,8 @@ if (use_v8_in_net && !is_android) {
     sources = [
       "dns/host_resolver_mojo.cc",
       "dns/host_resolver_mojo.h",
+      "proxy/mojo_proxy_resolver_factory.cc",
+      "proxy/mojo_proxy_resolver_factory.h",
       "proxy/mojo_proxy_resolver_impl.cc",
       "proxy/mojo_proxy_resolver_impl.h",
     ]
@@ -1378,6 +1380,7 @@ if (!is_android && !is_win && !is_mac) {
       sources -= [
         "dns/host_resolver_mojo_unittest.cc",
         "dns/mojo_host_resolver_impl_unittest.cc",
+        "proxy/mojo_proxy_resolver_factory_unittest.cc",
         "proxy/mojo_proxy_resolver_impl_unittest.cc",
       ]
     }