Correctly set root_library based on the application script URI instead of looking for the library t…

utils/kernel-service/kernel-service.dart

Index: utils/kernel-service/kernel-service.dart
diff --git a/utils/kernel-service/kernel-service.dart b/utils/kernel-service/kernel-service.dart
index 5b7ca5031c378a729bd9740d5777ef6e21fe4d27..f339296645bc2d43c5506c38b997b7c1737235a1 100644
--- a/utils/kernel-service/kernel-service.dart
+++ b/utils/kernel-service/kernel-service.dart
@@ -48,9 +48,13 @@ Future _processLoadRequest(request) async {
   final String inputFileUri = request[2];
   final Uri script = Uri.base.resolve(inputFileUri);
 
-  FileSystem fileSystem = request.length > 3
-      ? _buildFileSystem(request[3])
-      : PhysicalFileSystem.instance;
+  FileSystem fileSystem = PhysicalFileSystem.instance;
+  bool requireMain = true;
+
+  if (request.length > 3) {
+    fileSystem = _buildFileSystem(request[3]);
+    requireMain = false;
+  }
 
   Uri packagesUri = (Platform.packageConfig != null)
       ? Uri.parse(Platform.packageConfig)
@@ -82,7 +86,10 @@ Future _processLoadRequest(request) async {
 
   CompilationResult result;
   try {
-    Program program = await kernelForProgram(script, options);
+    Program program = requireMain
+        ? await kernelForProgram(script, options)
+        : await kernelForBuildUnit([script], options..chaseDependencies = true);
+
     if (errors.isNotEmpty) {
       result = new CompilationResult.errors(errors);
     } else {