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

pkg/compiler/lib/src/cps_ir/constant_propagation.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.
 
 part of dart2js.optimizers;
 
 /**
  * Propagates constants throughout the IR, and replaces branches with fixed
  * jumps as well as side-effect free expressions with known constant results.
  * Should be followed by the [ShrinkingReducer] pass.
@@ skipping 10 matching lines @@
   // arguments.
   final dart2js.ConstantSystem _constantSystem;
 
   ConstantPropagator(this._compiler, this._constantSystem);
 
   void rewrite(FunctionDefinition root) {
     if (root.isAbstract) return;
 
     // Set all parent pointers.
 
-    new _ParentVisitor().visit(root);
+    new ParentVisitor().visit(root);
 
     // Analyze. In this phase, the entire term is analyzed for reachability
     // and the constant status of each expression.
 
     _ConstPropagationVisitor analyzer =
         new _ConstPropagationVisitor(_compiler, _constantSystem);
     analyzer.analyze(root);
 
     // Transform. Uses the data acquired in the previous analysis phase to
     // replace branches with fixed targets and side-effect-free expressions
@@ skipping 615 matching lines @@
       return that;
     }
 
     if (this.constant == that.constant) {
       return this;
     }
 
     return NonConst;
   }
 }