Dart: Simplifies the handle watcher. Various cleanups and bugfixes.

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 8725b354105a0aa20e98aa3b9822675f6deec076..7017645513194725c493a2e9b0b82b84c5656970 100644
--- a/mojo/dart/embedder/BUILD.gn
+++ b/mojo/dart/embedder/BUILD.gn
@@ -7,11 +7,22 @@ action("generate_snapshot_bin") {
     "//dart/runtime/bin:gen_snapshot",
   ]
   inputs = [
+    "snapshot.dart",
     "//dart/runtime/tools/create_snapshot_bin.py",
     "//mojo/dart/embedder/builtin.dart",
     "//mojo/public/dart/bindings.dart",
     "//mojo/public/dart/core.dart",
-    "snapshot.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/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/timer_impl.dart",
+    "//mojo/public/dart/src/timer_queue.dart",
+    "//mojo/public/dart/src/types.dart",
   ]
   output = "$target_gen_dir/snapshot_gen.bin"
   outputs = [