Make Tracing Service not use outgoing InterfaceProvider, update conventions

services/tracing/public/cpp/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("cpp") {
   sources = [
+    "provider.cc",
+    "provider.h",
     "switches.cc",
     "switches.h",
-    "trace_provider_impl.cc",
-    "trace_provider_impl.h",
-    "tracing_impl.cc",
-    "tracing_impl.h",
   ]
 
   deps = [
     "//base",
     "//mojo/public/cpp/bindings",
     "//services/shell/public/cpp",
     "//services/tracing/public/interfaces",
   ]
 }