cps-ir: Split up main codegen and add a bailout exception to print out

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

Index: pkg/compiler/lib/src/cps_ir/cps_ir_builder_visitor.dart
diff --git a/pkg/compiler/lib/src/cps_ir/cps_ir_builder_visitor.dart b/pkg/compiler/lib/src/cps_ir/cps_ir_builder_visitor.dart
index ab2d17b19cde9e70f2761b682aba56cdee774d6b..90f97e2114c335e7435a8b0bdf0d0438b592e449 100644
--- a/pkg/compiler/lib/src/cps_ir/cps_ir_builder_visitor.dart
+++ b/pkg/compiler/lib/src/cps_ir/cps_ir_builder_visitor.dart
@@ -41,10 +41,7 @@ class IrBuilderTask extends CompilerTask {
       SourceFile sourceFile = elementSourceFile(element);
       IrBuilderVisitor builder =
           new IrBuilderVisitor(elementsMapping, compiler, sourceFile);
-      ir.FunctionDefinition function;
-      function = builder.buildFunction(element);
-
-      return function;
+      return builder.buildFunction(element);
     });
   }