Refactor SkyShell to allow multiple SkyViews

sky/shell/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.
 
 common_deps = [
   "//base",
   "//base:i18n",
   "//build/config/sanitizers:deps",
   "//dart/runtime:libdart",
   "//mojo/common",
@@ skipping 38 matching lines @@
       "android/tracing_controller.cc",
       "android/tracing_controller.h",
       "gpu/ganesh_context.cc",
       "gpu/ganesh_context.h",
       "gpu/ganesh_surface.cc",
       "gpu/ganesh_surface.h",
       "gpu/rasterizer.cc",
       "gpu/rasterizer.h",
       "gpu_delegate.cc",
       "gpu_delegate.h",
+      "instance.cc",
+      "instance.h",
       "platform_view.cc",
       "platform_view.h",
       "service_provider.h",
       "shell.cc",
       "shell.h",
       "ui/animator.cc",
       "ui/animator.h",
       "ui/engine.cc",
       "ui/engine.h",
       "ui/input_event_converter.cc",
@@ skipping 104 matching lines @@
     }
 
     deps = [
       ":$scaffolding_target",
       ":sky_resources",
     ]
   }
 } else {
   assert(false, "Unsupported platform")
 }