dart2js cps: Inline constructor bodies that are only called once.

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

 // Copyright (c) 2015, 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 cps_ir.optimization.inline;
 
 import 'cps_fragment.dart';
 import 'cps_ir_builder.dart' show ThisParameterLocal;
 import 'cps_ir_nodes.dart';
 import 'optimizers.dart';
@@ skipping 167 matching lines @@
 
   final CpsFunctionCompiler functionCompiler;
 
   final InliningCache cache = new InliningCache();
 
   final List<StackEntry> stack = <StackEntry>[];
 
   Inliner(this.functionCompiler);
 
   bool isCalledOnce(Element element) {
+    if (element is ConstructorBodyElement) {
+      ClassElement class_ = element.enclosingClass;
+      return !functionCompiler.compiler.world.hasAnyStrictSubclass(class_) &&
+          class_.constructors.tail?.isEmpty ?? false;
+    }
     return functionCompiler.compiler.typesTask.typesInferrer.isCalledOnce(
         element);
   }
 
   void rewrite(FunctionDefinition node, [CallStructure callStructure]) {
     ExecutableElement function = node.element;
 
     // Inlining in asynchronous or generator functions is disabled.  Inlining
     // triggers a bug in the async rewriter.
     // TODO(kmillikin): Fix the bug and eliminate this restriction if it makes
@@ skipping 412 matching lines @@
         (enclosingClass == backend.helpers.jsNumberClass ||
          enclosingClass == backend.helpers.jsDoubleClass ||
          enclosingClass == backend.helpers.jsIntClass)) {
       // These should be handled by operator specialization.
       return true;
     }
     if (target == backend.helpers.stringInterpolationHelper) return true;
     return false;
   }
 }