Port sky_shell to Linux for testing

sky/shell/BUILD.gn

Index: sky/shell/BUILD.gn
diff --git a/sky/shell/BUILD.gn b/sky/shell/BUILD.gn
index 0299d77428137c4cc2613c04b2f4f789eb1c619f..b28c8f8bdfe0efdb13868802a601a6cde36c6174 100644
--- a/sky/shell/BUILD.gn
+++ b/sky/shell/BUILD.gn
@@ -37,6 +37,7 @@ source_set("common") {
     "gpu_delegate.h",
     "platform_view.cc",
     "platform_view.h",
+    "service_provider.cc",
     "service_provider.h",
     "shell.cc",
     "shell.h",
@@ -169,6 +170,18 @@ if (is_android) {
       ":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")
 }