Add type inference for assert statements.

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 304165bd5bc5dbaa6a5091a9872cab7ca21e9932..1362b32f57d4b31a1f42b43569d142a32109649c 100644
--- a/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
@@ -2666,7 +2666,7 @@ class BodyBuilder extends ScopeListener<JumpTarget> implements BuilderHelper {
     debugEvent("Assert");
     Expression message = popForValueIfNotNull(commaToken);
     Expression condition = popForValue();
-    AssertStatement statement = new AssertStatement(condition,
+    AssertStatement statement = new KernelAssertStatement(condition,
         conditionStartOffset: leftParenthesis.offset + 1,
         conditionEndOffset: rightParenthesis.offset,
         message: message);