Expose some sky_viewer plumbing to allow for reuse

sky/viewer/BUILD.gn

 # Copyright 2014 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.
 
 import("//mojo/public/mojo_application.gni")
 import("//mojo/public/tools/bindings/mojom.gni")
 
-mojo_native_application("viewer") {
-  output_name = "sky_viewer"
-
+source_set("lib") {
   sources = [
-    "content_handler_impl.cc",
-    "content_handler_impl.h",
     "converters/basic_types.cc",
     "converters/basic_types.h",
     "converters/input_event_types.cc",
     "converters/input_event_types.h",
     "document_view.cc",
     "document_view.h",
     "internals.cc",
     "internals.h",
     "runtime_flags.cc",
     "runtime_flags.h",
-    "viewer.cc",
+    "sky_loader.cc",
+    "sky_loader.h",
+    "sky_viewer_base.cc",
+    "sky_viewer_base.h",
   ]
 
   include_dirs = [ ".." ]
 
   deps = [
     "//mojo/application",
     "//mojo/common",
     "//mojo/common:tracing_impl",
     "//mojo/converters/geometry",
     "//mojo/converters/input_events",
     "//mojo/converters/surfaces",
     "//mojo/icu",
-    "//mojo/public/cpp/bindings",
     "//mojo/public/cpp/system",
-    "//mojo/public/cpp/utility",
     "//mojo/public/interfaces/application",
     "//mojo/services/content_handler/public/interfaces",
     "//mojo/services/gpu/public/interfaces",
     "//mojo/services/input_events/public/interfaces",
     "//mojo/services/navigation/public/interfaces",
     "//mojo/services/network/public/interfaces",
     "//mojo/services/service_registry/public/interfaces",
     "//mojo/services/surfaces/public/interfaces",
-    "//mojo/services/view_manager/public/cpp",
     "//mojo/services/view_manager/public/interfaces",
     "//skia",
     "//sky/compositor",
     "//sky/engine",
     "//sky/engine/tonic",
     "//sky/services/platform",
     "//sky/services/testing:bindings",
     "//third_party/icu",
     "//ui/events",
     "//url",
   ]
+
+  public_deps = [
+    "//mojo/services/view_manager/public/cpp",
+  ]
 }
+
+mojo_native_application("viewer") {
+  output_name = "sky_viewer"
+
+  sources = [
+    "content_handler_impl.cc",
+    "content_handler_impl.h",
+    "viewer.cc",
+  ]
+
+  include_dirs = [ ".." ]
+
+  deps = [
+    ":lib",
+    "//base",
+    "//mojo/application",
+    "//mojo/public/cpp/bindings",
+    "//mojo/public/cpp/utility",
+    "//mojo/public/interfaces/application",
+    "//mojo/services/content_handler/public/interfaces",
+    "//mojo/services/network/public/interfaces",
+  ]
+}