Port touch-demo.sky to Dart and make it work in SkyShell

sky/services/viewport/BUILD.gn

Index: sky/services/viewport/BUILD.gn
diff --git a/mojo/services/console/public/interfaces/BUILD.gn b/sky/services/viewport/BUILD.gn
similarity index 56%
copy from mojo/services/console/public/interfaces/BUILD.gn
copy to sky/services/viewport/BUILD.gn
index 5378a4df14c650068e5606422f763deca7784285..0e024d4ef3fdf2961f2c3d6ef0c5bcc6447cbc6e 100644
--- a/mojo/services/console/public/interfaces/BUILD.gn
+++ b/sky/services/viewport/BUILD.gn
@@ -2,11 +2,11 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-import("../../../mojo_sdk_root.gni")
-import("$mojo_sdk_root/mojo/public/tools/bindings/mojom.gni")
+import("//mojo/public/tools/bindings/mojom.gni")
 
-mojom("interfaces") {
+mojom("viewport") {
   sources = [
-    "console.mojom",
+    "input_event.mojom",
+    "viewport_observer.mojom",
   ]
 }