Compile spawnUri entrypoints to JS with pub build/serve.

sdk/lib/_internal/pub/lib/src/dart.dart

Index: sdk/lib/_internal/pub/lib/src/dart.dart
diff --git a/sdk/lib/_internal/pub/lib/src/dart.dart b/sdk/lib/_internal/pub/lib/src/dart.dart
index af2c409263a6ae267ad32ef6d0e2ee780bb42597..481e124dbe6485f940908b9a49c8029e5bf94d75 100644
--- a/sdk/lib/_internal/pub/lib/src/dart.dart
+++ b/sdk/lib/_internal/pub/lib/src/dart.dart
@@ -107,11 +107,14 @@ String get _libPath {
 
 /// Returns whether [dart] looks like an entrypoint file.
 bool isEntrypoint(CompilationUnit dart) {
+  // Allow two or fewer arguments so that entrypoints intended for use with
+  // [spawnUri] get counted.
+  //
   // TODO(nweiz): this misses the case where a Dart file doesn't contain main(),
   // but it parts in another file that does.
   return dart.declarations.any((node) {
     return node is FunctionDeclaration && node.name.name == "main" &&
-        node.functionExpression.parameters.parameters.isEmpty;
+        node.functionExpression.parameters.parameters.length <= 2;
   });
 }