[CLI] Fix handling of --timeline-streams when it is supplied after dart run

--timeline-streams has been listed in the "options implied by --observe"
section of the dart run help messages, but it has been getting ignored.
This CL fixes that problem.

TEST=manual testing, CI

Change-Id: Ib6c2425a2681b61375df186673e0f195e3fae580
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/288581
Reviewed-by: Ben Konyi <bkonyi@google.com>

pkg/dartdev/test/commands/run_test.dart

@@ -323,6 +323,31 @@ void main(List<String> args) => print("$b $args");
     expect(result.exitCode, 0);
   });
 
+  test('with accepted VM flags related to the timeline', () async {
+    p = project(
+        mainSrc: 'import "dart:developer";'
+            'void main() {'
+            'Timeline.startSync("sync");'
+            'Timeline.finishSync();'
+            '}');
+
+    final result = await p.run([
+      '--timeline-recorder=file',
+      'run',
+      '--timeline-streams=Dart',
+      p.relativeFilePath
+    ]);
+
+    expect(result.stderr, isEmpty);
+    expect(result.stdout, isEmpty);
+    expect(result.exitCode, 0);
+    expect(
+        p
+            .findFile(path.join(p.dirPath, 'dart-timeline.json'))!
+            .readAsStringSync(),
+        contains('"name":"sync","cat":"Dart"'));
+  });
+
   test('fails when provided verbose VM flags', () async {
     p = project(mainSrc: "void main() { print('Hello World'); }");
 

runtime/bin/main_options.cc

@@ -416,6 +416,7 @@ bool Options::ProcessVMDebuggingOptions(const char* arg,
   V("--no-pause-isolates-on-unhandled-exception", arg)                         \
   V("--warn-on-pause-with-no-debugger", arg)                                   \
   V("--no-warn-on-pause-with-no-debugger", arg)                                \
+  V("--timeline-streams", arg)                                                 \
   V("--enable-experiment", arg)
   HANDLE_DARTDEV_VM_DEBUG_OPTIONS(IS_DEBUG_OPTION, arg);