cps_ir: Add JS checks, use argument nullability

pkg/compiler/lib/src/tree_ir/tree_ir_nodes.dart

 // Copyright (c) 2014, 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.
 
 library tree_ir_nodes;
 
 import '../constants/values.dart' as values;
 import '../dart_types.dart' show DartType, InterfaceType, TypeVariableType;
 import '../elements/elements.dart';
 import '../io/source_information.dart' show SourceInformation;
@@ skipping 847 matching lines @@
   accept1(ExpressionVisitor1 visitor, arg) {
     return visitor.visitInterceptor(this, arg);
   }
 }
 
 class ForeignCode extends Node {
   final js.Template codeTemplate;
   final types.TypeMask type;
   final List<Expression> arguments;
   final native.NativeBehavior nativeBehavior;
+  final List<bool> nullableArguments;  // One 'bit' per argument.
   final Element dependency;
 
   ForeignCode(this.codeTemplate, this.type, this.arguments, this.nativeBehavior,
-      this.dependency);
+      this.nullableArguments, this.dependency) {
+    assert(arguments.length == nullableArguments.length);
+  }
 }
 
 class ForeignExpression extends ForeignCode implements Expression {
-  ForeignExpression(js.Template codeTemplate, types.TypeMask type,
+  ForeignExpression(
+      js.Template codeTemplate, types.TypeMask type,
       List<Expression> arguments, native.NativeBehavior nativeBehavior,
+      List<bool> nullableArguments,
       Element dependency)
-      : super(codeTemplate, type, arguments, nativeBehavior,
+      : super(codeTemplate, type, arguments, nativeBehavior, nullableArguments,
           dependency);
 
   accept(ExpressionVisitor visitor) {
     return visitor.visitForeignExpression(this);
   }
 
   accept1(ExpressionVisitor1 visitor, arg) {
     return visitor.visitForeignExpression(this, arg);
   }
 }
 
 class ForeignStatement extends ForeignCode implements Statement {
-  ForeignStatement(js.Template codeTemplate, types.TypeMask type,
+  ForeignStatement(
+      js.Template codeTemplate, types.TypeMask type,
       List<Expression> arguments, native.NativeBehavior nativeBehavior,
+      List<bool> nullableArguments,
       Element dependency)
-      : super(codeTemplate, type, arguments, nativeBehavior,
+      : super(codeTemplate, type, arguments, nativeBehavior, nullableArguments,
           dependency);
 
   accept(StatementVisitor visitor) {
     return visitor.visitForeignStatement(this);
   }
 
   accept1(StatementVisitor1 visitor, arg) {
     return visitor.visitForeignStatement(this, arg);
   }
 
@@ skipping 695 matching lines @@
 
   /// Number of uses of the current fallthrough target.
   int get useCount => _stack.last.useCount;
 
   /// Indicate that a statement will fall through to the current fallthrough
   /// target.
   void use() {
     ++_stack.last.useCount;
   }
 }