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

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

Index: pkg/compiler/lib/src/cps_ir/shrinking_reductions.dart
diff --git a/pkg/compiler/lib/src/cps_ir/shrinking_reductions.dart b/pkg/compiler/lib/src/cps_ir/shrinking_reductions.dart
index f14ece5a98f9ee8b123bee06c896fb666b410602..f21b1b1e3837340e8d2e292b40f688b23cc594ce 100644
--- a/pkg/compiler/lib/src/cps_ir/shrinking_reductions.dart
+++ b/pkg/compiler/lib/src/cps_ir/shrinking_reductions.dart
@@ -22,7 +22,7 @@ class ShrinkingReducer implements Pass {
     _redexVisitor = new _RedexVisitor(_worklist);
 
     // Set all parent pointers.
-    new _ParentVisitor().visit(root);
+    new ParentVisitor().visit(root);
 
     // Sweep over the term, collecting redexes into the worklist.
     _redexVisitor.visitFunctionDefinition(root);
@@ -293,7 +293,7 @@ class _RemovalRedexVisitor extends _RedexVisitor {
 }
 
 /// Traverses the CPS term and sets node.parent for each visited node.
-class _ParentVisitor extends RecursiveVisitor {
+class ParentVisitor extends RecursiveVisitor {
 
   processFunctionDefinition(FunctionDefinition node) {
     node.body.parent = node;