Move 'dart:mojo.internal' into sdk_ext directory of mojo package

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 0f425aec2f779d0c8e0d8be68214faef41f9cdf2..c15947241eac39fa087433be937f250c946819d0 100644
--- a/mojo/dart/embedder/BUILD.gn
+++ b/mojo/dart/embedder/BUILD.gn
@@ -103,7 +103,6 @@ action_foreach("dart_embedder_package_sdk") {
     "//mojo/public/dart/lib/application.dart",
     "//mojo/public/dart/lib/bindings.dart",
     "//mojo/public/dart/lib/core.dart",
-    "//mojo/public/dart/lib/internal.dart",
     "//mojo/public/dart/lib/src/application.dart",
     "//mojo/public/dart/lib/src/application_connection.dart",
     "//mojo/public/dart/lib/src/buffer.dart",
@@ -113,15 +112,16 @@ action_foreach("dart_embedder_package_sdk") {
     "//mojo/public/dart/lib/src/drain_data.dart",
     "//mojo/public/dart/lib/src/event_stream.dart",
     "//mojo/public/dart/lib/src/handle.dart",
-    "//mojo/public/dart/lib/src/handle_watcher.dart",
     "//mojo/public/dart/lib/src/message.dart",
     "//mojo/public/dart/lib/src/message_pipe.dart",
-    "//mojo/public/dart/lib/src/natives.dart",
     "//mojo/public/dart/lib/src/proxy.dart",
     "//mojo/public/dart/lib/src/struct.dart",
     "//mojo/public/dart/lib/src/stub.dart",
-    "//mojo/public/dart/lib/src/timer_queue.dart",
     "//mojo/public/dart/lib/src/types.dart",
+    "//mojo/public/dart/sdk_ext/internal.dart",
+    "//mojo/public/dart/sdk_ext/src/handle_watcher.dart",
+    "//mojo/public/dart/sdk_ext/src/natives.dart",
+    "//mojo/public/dart/sdk_ext/src/timer_queue.dart",
   ]
   outputs = [
     "$root_gen_dir/dart_embedder_packages/{{source_root_relative_dir}}/{{source_file_part}}",
@@ -298,11 +298,11 @@ action("generate_snapshot_bin") {
     "//dart/runtime/tools/create_snapshot_bin.py",
     "//mojo/dart/embedder/builtin.dart",
     "//mojo/dart/embedder/packages.dart",
-    "//mojo/public/dart/lib/internal.dart",
     "//mojo/public/dart/lib/io.dart",
-    "//mojo/public/dart/lib/src/handle_watcher.dart",
-    "//mojo/public/dart/lib/src/natives.dart",
-    "//mojo/public/dart/lib/src/timer_queue.dart",
+    "//mojo/public/dart/sdk_ext/internal.dart",
+    "//mojo/public/dart/sdk_ext/src/handle_watcher.dart",
+    "//mojo/public/dart/sdk_ext/src/natives.dart",
+    "//mojo/public/dart/sdk_ext/src/timer_queue.dart",
   ]
   vm_isolate_snapshot = "$target_gen_dir/vm_isolate_snapshot.bin"
   isolate_snapshot = "$target_gen_dir/isolate_snapshot.bin"
@@ -316,7 +316,7 @@ action("generate_snapshot_bin") {
                      "root_out_dir")
   script = "//dart/runtime/tools/create_snapshot_bin.py"
   builtin_path = rebase_path("//mojo/dart/embedder/builtin.dart")
-  internal_path = rebase_path("//mojo/public/dart/lib/internal.dart")
+  internal_path = rebase_path("//mojo/public/dart/sdk_ext/internal.dart")
   io_path = rebase_path("//mojo/public/dart/lib/io.dart")
 
   embedder_packages_path = rebase_path("//mojo/dart/embedder/packages.dart")