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

sky/engine/bindings/BUILD.gn

Index: sky/engine/bindings/BUILD.gn
diff --git a/sky/engine/bindings/BUILD.gn b/sky/engine/bindings/BUILD.gn
index 71951bd5a916d34020b9e93a740725554a873265..105221bf2fdc6dd46260d256a73901af5b5be080 100644
--- a/sky/engine/bindings/BUILD.gn
+++ b/sky/engine/bindings/BUILD.gn
@@ -61,10 +61,10 @@ action("generate_snapshot_bin") {
   inputs = [
     "//dart/runtime/tools/create_snapshot_bin.py",
     "//sky/engine/bindings/builtin.dart",
-    "//mojo/public/dart/lib/internal.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",
     "snapshot.dart",
   ]
   vm_isolate_snapshot = "$target_gen_dir/vm_isolate_snapshot.bin"
@@ -76,7 +76,7 @@ action("generate_snapshot_bin") {
 
   builtin_path = rebase_path("//sky/engine/bindings/builtin.dart")
   dart_sky_path = rebase_path("$bindings_output_dir/dart_sky.dart")
-  internal_path = rebase_path("//mojo/public/dart/lib/internal.dart")
+  internal_path = rebase_path("//mojo/public/dart/sdk_ext/internal.dart")
 
   gen_snapshot_dir =
       get_label_info("//dart/runtime/bin:gen_snapshot($host_toolchain)",