Remove BackendClasses and JavaScriptBackendClasses.

pkg/compiler/lib/src/ssa/optimize.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 '../common/codegen.dart' show CodegenRegistry, CodegenWorkItem;
 import '../common/names.dart' show Selectors;
 import '../common/tasks.dart' show CompilerTask;
 import '../compiler.dart' show Compiler;
 import '../constants/constant_system.dart';
 import '../constants/values.dart';
@@ skipping 150 matching lines @@
 /// Returns `true` if [mask] represents only types that have a length that
 /// cannot change.  The current implementation is conservative for the purpose
 /// of identifying gvn-able lengths and mis-identifies some unions of fixed
 /// length indexables (see TODO) as not fixed length.
 bool isFixedLength(mask, ClosedWorld closedWorld) {
   if (mask.isContainer && mask.length != null) {
     // A container on which we have inferred the length.
     return true;
   }
   // TODO(sra): Recognize any combination of fixed length indexables.
-  if (mask.containsOnly(closedWorld.backendClasses.fixedListClass) ||
-      mask.containsOnly(closedWorld.backendClasses.constListClass) ||
+  if (mask.containsOnly(closedWorld.commonElements.jsFixedArrayClass) ||
+      mask.containsOnly(closedWorld.commonElements.jsUnmodifiableArrayClass) ||
       mask.containsOnlyString(closedWorld) ||
       closedWorld.commonMasks.isTypedArray(mask)) {
     return true;
   }
   return false;
 }
 
 /**
  * If both inputs to known operations are available execute the operation at
  * compile-time.
@@ skipping 2678 matching lines @@
 
     keyedValues.forEach((receiver, values) {
       result.keyedValues[receiver] =
           new Map<HInstruction, HInstruction>.from(values);
     });
 
     result.nonEscapingReceivers.addAll(nonEscapingReceivers);
     return result;
   }
 }