Revert "Revert "Make ClosureTask only accept Element-level APIs instead of resolvedAst.""

pkg/compiler/lib/src/inferrer/builder_kernel.dart

Index: pkg/compiler/lib/src/inferrer/builder_kernel.dart
diff --git a/pkg/compiler/lib/src/inferrer/builder_kernel.dart b/pkg/compiler/lib/src/inferrer/builder_kernel.dart
index dd06c8b9f5d93d1118747c3f19cbce375ecc10c3..1e2f9a69a1213a713666ce93937901742552ea0b 100644
--- a/pkg/compiler/lib/src/inferrer/builder_kernel.dart
+++ b/pkg/compiler/lib/src/inferrer/builder_kernel.dart
@@ -103,8 +103,8 @@ class KernelTypeGraphBuilder extends ir.Visitor<TypeInformation> {
     // be handled specially, in that we are computing their LUB at
     // each update, and reading them yields the type that was found in a
     // previous analysis of [outermostElement].
-    ClosureClassMap closureData =
-        compiler.closureToClassMapper.getClosureToClassMapping(resolvedAst);
+    ClosureClassMap closureData = compiler.closureToClassMapper
+        .getClosureToClassMapping(resolvedAst.element);
     closureData.forEachCapturedVariable((variable, field) {
       locals.setCaptured(variable, field);
     });