dart2js: get:hashCode methods to avoid Object.hashCode

pkg/compiler/lib/src/ssa/builder.dart

 // Copyright (c) 2012, 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.
 
 import 'dart:collection';
 
 import 'package:js_runtime/shared/embedded_names.dart';
 
 import '../closure.dart';
 import '../common.dart';
@@ skipping 64 matching lines @@
 }
 
 /// A synthetic local variable only used with the SSA graph.
 ///
 /// For instance used for holding return value of function or the exception of a
 /// try-catch statement.
 class SyntheticLocal extends Local {
   final String name;
   final ExecutableElement executableContext;
 
+  // Avoid slow Object.hashCode.
+  final int hashCode = _nextHashCode = (_nextHashCode + 1).toUnsigned(30);
+  static int _nextHashCode = 0;
+
   SyntheticLocal(this.name, this.executableContext);
 
   toString() => 'SyntheticLocal($name)';
 }
 
 class SsaBuilderTask extends CompilerTask {
   final CodeEmitterTask emitter;
   final JavaScriptBackend backend;
   final SourceInformationStrategy sourceInformationFactory;
   final Compiler compiler;
@@ skipping 8531 matching lines @@
   const _LoopTypeVisitor();
   int visitNode(ast.Node node) => HLoopBlockInformation.NOT_A_LOOP;
   int visitWhile(ast.While node) => HLoopBlockInformation.WHILE_LOOP;
   int visitFor(ast.For node) => HLoopBlockInformation.FOR_LOOP;
   int visitDoWhile(ast.DoWhile node) => HLoopBlockInformation.DO_WHILE_LOOP;
   int visitAsyncForIn(ast.AsyncForIn node) => HLoopBlockInformation.FOR_IN_LOOP;
   int visitSyncForIn(ast.SyncForIn node) => HLoopBlockInformation.FOR_IN_LOOP;
   int visitSwitchStatement(ast.SwitchStatement node) =>
       HLoopBlockInformation.SWITCH_CONTINUE_LOOP;
 }