Plumb extra 'requireMain' flag through kernel builder entry point.

This is the method used by dart2wasm to generate a kernel from a source URI. For dynamic modules, the source will, by design, not include a 'main' function.

Without this flag the CFE will exit early with an error while compiling the source.

Change-Id: I1b66f7c0052ead80f5e555555d19a1b8a0cb590f
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/400920
Reviewed-by: Johnni Winther <[email protected]>
Commit-Queue: Nate Biggs <[email protected]>

Author: natebiggs

pkg/front_end/lib/src/api_prototype/kernel_generator.dart

@@ -42,9 +42,10 @@ import 'compiler_options.dart' show CompilerOptions;
 /// an error is reported.
 // TODO(sigmund): rename to kernelForScript?
 Future<CompilerResult?> kernelForProgram(Uri source, CompilerOptions options,
-    {List<Uri> additionalSources = const <Uri>[]}) async {
+    {List<Uri> additionalSources = const <Uri>[],
+    bool requireMain = true}) async {
   return (await kernelForProgramInternal(source, options,
-      additionalSources: additionalSources));
+      additionalSources: additionalSources, requireMain: requireMain));
 }
 
 // Coverage-ignore(suite): Not run.