Make identical an external function and make it throw in both runtimes, as they both recognize it.

sdk/lib/_internal/compiler/implementation/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.
 
 part of ssa;
 
 /**
  * A special element for the extra parameter taken by intercepted
  * methods. We need to override [Element.computeType] because our
  * optimizers may look at its declared type.
@@ skipping 3352 matching lines @@
       // TODO(5347): Try to avoid the need for calling [implementation] before
       // calling [addStaticSendArgumentsToList].
       bool succeeded = addStaticSendArgumentsToList(selector, node.arguments,
                                                     element.implementation,
                                                     inputs);
       if (!succeeded) {
         generateWrongArgumentCountError(node, element, node.arguments);
         return;
       }
 
-      // TODO(kasperl): Try to use the general inlining infrastructure for
-      // inlining the identical function.
       if (identical(element, compiler.identicalFunction)) {
         pushWithPosition(new HIdentity(target, inputs[1], inputs[2]), node);
         return;
       }
 
       HInvokeStatic instruction = new HInvokeStatic(inputs);
       // TODO(ngeoffray): Only do this if knowing the return type is
       // useful.
       HType returnType =
           builder.backend.optimisticReturnTypesWithRecompilationOnTypeChange(
@@ skipping 1606 matching lines @@
           new HSubGraphBlockInformation(elseBranch.graph));
 
     HBasicBlock conditionStartBlock = conditionBranch.block;
     conditionStartBlock.setBlockFlow(info, joinBlock);
     SubGraph conditionGraph = conditionBranch.graph;
     HIf branch = conditionGraph.end.last;
     assert(branch is HIf);
     branch.blockInformation = conditionStartBlock.blockFlow;
   }
 }