Populate TypeInferrerImpl.closureContext more frequently.

pkg/front_end/lib/src/fasta/kernel/body_builder.dart

Index: pkg/front_end/lib/src/fasta/kernel/body_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/kernel/body_builder.dart b/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
index ff6d4eb0013035c9182867770f0074c68f32a997..a1b7644923ab7838405164d8afa1971208afc438 100644
--- a/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
@@ -467,7 +467,8 @@ class BodyBuilder extends ScopeListener<JumpTarget> implements BuilderHelper {
       FormalParameters formals, AsyncMarker asyncModifier, Statement body) {
     debugEvent("finishFunction");
     typePromoter.finished();
-    _typeInferrer.inferStatement(body);
+    // TODO(paulberry): get function return type from the outline.
+    _typeInferrer.inferFunctionBody(null, asyncModifier, body);
     KernelFunctionBuilder builder = member;
     builder.body = body;
     if (formals?.optional != null) {