cps-ir: Implement boolean conversion in and use it to implement '&&', '||', and '?:'.

pkg/compiler/lib/src/cps_ir/cps_ir_nodes.dart

 // Copyright (c) 2013, 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.
 
 // IrNodes are kept in a separate library to have precise control over their
 // dependencies on other parts of the system.
 library dart2js.ir_nodes;
 
 import '../constants/expressions.dart';
 import '../constants/values.dart' as values show ConstantValue;
@@ skipping 562 matching lines @@
   /// If `true`, [body] and [returnContinuation] are `null` and [localConstants]
   /// is empty.
   bool get isAbstract => body == null;
 }
 
 List<Reference<Primitive>> _referenceList(Iterable<Primitive> definitions) {
   return definitions.map((e) => new Reference<Primitive>(e)).toList();
 }
 
 abstract class Visitor<T> {
+  const Visitor();
+
   T visit(Node node) => node.accept(this);
   // Abstract classes.
   T visitNode(Node node) => null;
   T visitExpression(Expression node) => visitNode(node);
   T visitDefinition(Definition node) => visitNode(node);
   T visitPrimitive(Primitive node) => visitDefinition(node);
   T visitCondition(Condition node) => visitNode(node);
 
   // Concrete classes.
   T visitFunctionDefinition(FunctionDefinition node) => visitNode(node);
@@ skipping 23 matching lines @@
   T visitParameter(Parameter node) => visitPrimitive(node);
   T visitContinuation(Continuation node) => visitDefinition(node);
 
   // Conditions.
   T visitIsTrue(IsTrue node) => visitCondition(node);
 }
 
 /// Recursively visits the entire CPS term, and calls abstract `process*`
 /// (i.e. `processLetPrim`) functions in pre-order.
 abstract class RecursiveVisitor extends Visitor {
+  const RecursiveVisitor();
+
   // Ensures that RecursiveVisitor contains overrides for all relevant nodes.
   // As a rule of thumb, nodes with structure to traverse should be overridden
   // with the appropriate visits in this class (for example, visitLetCont),
   // while leaving other nodes for subclasses (i.e., visitLiteralList).
   visitNode(Node node) {
     throw "RecursiveVisitor is stale, add missing visit overrides";
   }
 
   processReference(Reference ref) {}
 
@@ skipping 309 matching lines @@
       release(node.parameters[i]);
     }
   }
 
   void visitIsTrue(IsTrue node) {
     visitReference(node.value);
   }
 
 }