Update mojo sdk to rev c02a28868825edfa57ab77947b8cb15e741c5598

third_party/mojo/src/mojo/public/dart/BUILD.gn

 import("../mojo_sdk.gni")
 import("rules.gni")
 
 dart_mojo_sdk_sources = [
   "lib/application.dart",
   "lib/bindings.dart",
   "lib/core.dart",
   "lib/src/application_connection.dart",
   "lib/src/application.dart",
   "lib/src/buffer.dart",
   "lib/src/codec.dart",
   "lib/src/control_message.dart",
   "lib/src/data_pipe.dart",
   "lib/src/drain_data.dart",
   "lib/src/event_stream.dart",
   "lib/src/handle.dart",
   "lib/src/message.dart",
   "lib/src/message_pipe.dart",
   "lib/src/proxy.dart",
   "lib/src/struct.dart",
   "lib/src/stub.dart",
   "lib/src/union.dart",
   "lib/src/types.dart",
-  "sdk_ext/internal.dart",
-  "sdk_ext/src/handle_watcher.dart",
-  "sdk_ext/src/natives.dart",
-  "sdk_ext/src/timer_queue.dart",
 ]
 
 dartzip_package("dart") {
   sources = dart_mojo_sdk_sources + [
               "pubspec.yaml",
               "CHANGELOG.md",
               "README.md",
             ]
   uses_pub = true
   package_name_override = "mojo"
   deps = [
     "../interfaces/application",
     "../interfaces/bindings",
     "../interfaces/network",
   ]
 }
 
 dart_pkg("mojo") {
   sources = dart_mojo_sdk_sources + [
               "pubspec.yaml",
               "CHANGELOG.md",
               "README.md",
             ]
 
+  sdk_ext_directory = "sdk_ext"
+  sdk_ext_mappings = [ "dart:mojo.internal,internal.dart" ]
+
   # List of mojom targets that the mojo pkg exports
   deps = [
     "../interfaces",
   ]
 }