Dart: Adds a content handler and a test.

mojo/dart/embedder/BUILD.gn

Index: mojo/dart/embedder/BUILD.gn
diff --git a/mojo/dart/embedder/BUILD.gn b/mojo/dart/embedder/BUILD.gn
index 460515bde807bfec787a2f87b10806ba88a6e543..f91a2c0ccd126a75dab95b989544a3b38bdaadc9 100644
--- a/mojo/dart/embedder/BUILD.gn
+++ b/mojo/dart/embedder/BUILD.gn
@@ -5,6 +5,7 @@
 action("generate_snapshot_bin") {
   deps = [
     "//dart/runtime/bin:gen_snapshot",
+    "//mojo/public/interfaces/application",
   ]
   inputs = [
     "snapshot.dart",
@@ -12,14 +13,17 @@ action("generate_snapshot_bin") {
     "//mojo/dart/embedder/builtin.dart",
     "//mojo/public/dart/bindings.dart",
     "//mojo/public/dart/core.dart",
+    "//mojo/public/dart/src/application.dart",
     "//mojo/public/dart/src/buffer.dart",
     "//mojo/public/dart/src/client.dart",
     "//mojo/public/dart/src/codec.dart",
     "//mojo/public/dart/src/data_pipe.dart",
+    "//mojo/public/dart/src/drain_data.dart",
     "//mojo/public/dart/src/handle.dart",
     "//mojo/public/dart/src/handle_watcher.dart",
     "//mojo/public/dart/src/interface.dart",
     "//mojo/public/dart/src/message_pipe.dart",
+    "//mojo/public/dart/src/service_provider.dart",
     "//mojo/public/dart/src/timer_impl.dart",
     "//mojo/public/dart/src/timer_queue.dart",
     "//mojo/public/dart/src/types.dart",
@@ -33,14 +37,21 @@ action("generate_snapshot_bin") {
   builtin_path = rebase_path("//mojo/dart/embedder/builtin.dart")
   bindings_path = rebase_path("//mojo/public/dart/bindings.dart")
   core_path = rebase_path("//mojo/public/dart/core.dart")
+  app_interface_path = "$root_gen_dir/mojo/public/interfaces/application"
+  app_path = rebase_path("${app_interface_path}/application.mojom.dart")
+  sp_path = rebase_path("${app_interface_path}/service_provider.mojom.dart")
+  shell_path = rebase_path("${app_interface_path}/shell.mojom.dart")
   args = [
     "--executable", rebase_path("$root_out_dir/gen_snapshot"),
     "--script", rebase_path("snapshot.dart"),
     "--output_bin", rebase_path(output, root_build_dir),
     "--target_os", os,
+    "--url_mapping=dart:mojo_application,$app_path",
     "--url_mapping=dart:mojo_bindings,$bindings_path",
     "--url_mapping=dart:mojo_builtin,$builtin_path",
     "--url_mapping=dart:mojo_core,$core_path",
+    "--url_mapping=dart:mojo_service_provider,$sp_path",
+    "--url_mapping=dart:mojo_shell,$shell_path",
   ]
 }