Add interfaces for most major Blimp net components.

blimp/engine/net/BUILD.gn

 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-source_set("core") {
+source_set("net") {
   sources = [
-    "data_use_user_data.cc",
-    "data_use_user_data.h",
+    "engine_connection_manager.cc",
+    "engine_connection_manager.h",
   ]
+
   deps = [
     "//base",
     "//net",
   ]
 }