Port sky_shell to Linux for testing

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 19 matching lines @@
     "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",
     "platform_view.cc",
     "platform_view.h",
+    "service_provider.cc",
     "service_provider.h",
     "shell.cc",
     "shell.h",
     "shell_view.cc",
     "shell_view.h",
     "ui/animator.cc",
     "ui/animator.h",
     "ui/engine.cc",
     "ui/engine.h",
     "ui/input_event_converter.cc",
@@ skipping 112 matching lines @@
                ":common",
                "//sky/services/ns_net",
              ]
     }
 
     deps = [
       ":$scaffolding_target",
       ":sky_resources",
     ]
   }
+} else if (is_linux) {
+  executable("shell") {
+    output_name = "sky_shell"
+
+    sources = [
+      "linux/main.cc",
+      "linux/platform_service_provider_linux.cc",
+      "linux/platform_view_linux.cc",
+    ]
+
+    deps = common_deps + [ ":common" ]
+  }
 } else {
   assert(false, "Unsupported platform")
 }