Add type inference for assert statements.

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

 // Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /// This file declares a "shadow hierarchy" of concrete classes which extend
 /// the kernel class hierarchy, adding methods and fields needed by the
 /// BodyBuilder.
 ///
 /// Instances of these classes may be created using the factory methods in
 /// `ast_factory.dart`.
@@ skipping 72 matching lines @@
       KernelTypeInferrer inferrer, DartType typeContext, bool typeNeeded) {
     typeNeeded =
         inferrer.listener.asExpressionEnter(this, typeContext) || typeNeeded;
     inferrer.inferExpression(operand, null, false);
     var inferredType = typeNeeded ? type : null;
     inferrer.listener.asExpressionExit(this, inferredType);
     return inferredType;
   }
 }
 
+/// Concrete shadow object representing an assertion statement in kernel form.
+class KernelAssertStatement extends AssertStatement implements KernelStatement {
+  KernelAssertStatement(Expression condition,
+      {Expression message, int conditionStartOffset, int conditionEndOffset})
+      : super(condition,
+            message: message,
+            conditionStartOffset: conditionStartOffset,
+            conditionEndOffset: conditionEndOffset);
+
+  @override
+  void _inferStatement(KernelTypeInferrer inferrer) {
+    inferrer.listener.assertStatementEnter(this);
+    inferrer.inferExpression(condition, null, false);
+    if (message != null) {
+      inferrer.inferExpression(message, null, false);
+    }
+    inferrer.listener.assertStatementExit(this);
+  }
+}
+
 /// Shadow object for [AwaitExpression].
 class KernelAwaitExpression extends AwaitExpression
     implements KernelExpression {
   KernelAwaitExpression(Expression operand) : super(operand);
 
   @override
   void _collectDependencies(KernelDependencyCollector collector) {
     // Inference dependencies are the dependencies of the awaited expression.
     collector.collectDependencies(operand);
   }
@@ skipping 2110 matching lines @@
   }
 
   transformChildren(v) {
     return internalError("Internal error: Unsupported operation.");
   }
 
   visitChildren(v) {
     return internalError("Internal error: Unsupported operation.");
   }
 }