Allow --machine/--allow-embedding to be passed to devtools_tool serve (#6670)

* Allow --machine to be passed to devtools_tool serve

* Add allow-embedding

tool/lib/commands/serve.dart

diff --git a/tool/lib/commands/serve.dart b/tool/lib/commands/serve.dart
index cab9575..869abdf 100644
--- a/tool/lib/commands/serve.dart
+++ b/tool/lib/commands/serve.dart
@@ -14,6 +14,8 @@
 const _useLocalFlutterFlag = 'use-local-flutter';
 const _updatePerfettoFlag = 'update-perfetto';
 const _buildAppFlag = 'build-app';
+const _machineFlag = 'machine';
+const _allowEmbeddingFlag = 'allow-embedding';
 
 /// This command builds DevTools in release mode by running the
 /// `devtools_tool build-release` command and then serves DevTools with a
@@ -53,6 +55,16 @@
         help:
             'Whether to build the DevTools app in release mode before starting '
             'the DevTools server.',
+      )
+      // Flags defined in the server in DDS.
+      ..addFlag(
+        _machineFlag,
+        negatable: false,
+        help: 'Sets output format to JSON for consumption in tools.',
+      )
+      ..addFlag(
+        _allowEmbeddingFlag,
+        help: 'Allow embedding DevTools inside an iframe.',
       );
   }