Fix memory leak in test.

pkg/front_end/test/fasta/testing/suite.dart

Index: pkg/front_end/test/fasta/testing/suite.dart
diff --git a/pkg/front_end/test/fasta/testing/suite.dart b/pkg/front_end/test/fasta/testing/suite.dart
index c799b1f432d433cc20a0cbbaa79f444ffa8e31c7..1303ae9172af777810ed797291a06fb23619e96e 100644
--- a/pkg/front_end/test/fasta/testing/suite.dart
+++ b/pkg/front_end/test/fasta/testing/suite.dart
@@ -268,6 +268,7 @@ class Outline extends Step<TestDescription, Program, FastaContext> {
     } on InputError catch (e, s) {
       return fail(null, e.error, s);
     }
+    context.programToTarget.clear();
     context.programToTarget[p] = sourceTarget;
     return pass(p);
   }
@@ -280,6 +281,7 @@ class Transform extends Step<Program, Program, FastaContext> {
 
   Future<Result<Program>> run(Program program, FastaContext context) async {
     KernelTarget sourceTarget = context.programToTarget[program];
+    context.programToTarget.remove(program);
     TestVmFastaTarget backendTarget = sourceTarget.backendTarget;
     backendTarget.enabled = true;
     try {