Don't undo an interceptor optimization

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

 // Copyright (c) 2013, 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 '../common/codegen.dart' show CodegenWorkItem;
 import '../compiler.dart' show Compiler;
 import '../constants/constant_system.dart';
 import '../constants/values.dart';
 import '../elements/elements.dart';
 import '../js_backend/backend_helpers.dart' show BackendHelpers;
@@ skipping 282 matching lines @@
     }
 
     // Try computing a constant interceptor.
     HInstruction constantInterceptor =
         tryComputeConstantInterceptor(receiver, interceptedClasses);
     if (constantInterceptor != null) {
       node.block.rewrite(node, constantInterceptor);
       return false;
     }
 
+    // If it is a conditional constant interceptor and was not strengthened to a
+    // constant interceptor then there is nothing more we can do.
+    if (node.isConditionalConstantInterceptor) return false;
+
     // Do we have an 'almost constant' interceptor?  The receiver could be
     // `null` but not any other JavaScript falsy value, `null` values cause
     // `NoSuchMethodError`s, and if the receiver was not null we would have a
     // constant interceptor `C`.  Then we can use `(receiver && C)` for the
     // interceptor.
-    if (receiver.canBeNull() && !node.isConditionalConstantInterceptor) {
+    if (receiver.canBeNull()) {
       if (!interceptedClasses.contains(helpers.jsNullClass)) {
         // Can use `(receiver && C)` only if receiver is either null or truthy.
         if (!(receiver.canBePrimitiveNumber(compiler) ||
             receiver.canBePrimitiveBoolean(compiler) ||
             receiver.canBePrimitiveString(compiler))) {
           ClassElement interceptorClass = tryComputeConstantInterceptorFromType(
               receiver.instructionType.nonNullable(), interceptedClasses);
           if (interceptorClass != null) {
             HInstruction constantInstruction = graph.addConstant(
                 new InterceptorConstantValue(interceptorClass.thisType),
@@ skipping 96 matching lines @@
       instruction = new HInvokeDynamicMethod(
           selector, mask, inputs, node.instructionType, true);
     }
 
     HBasicBlock block = node.block;
     block.addAfter(node, instruction);
     block.rewrite(node, instruction);
     return true;
   }
 }