Remove BackendClasses and JavaScriptBackendClasses.

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

Index: pkg/compiler/lib/src/ssa/invoke_dynamic_specializers.dart
diff --git a/pkg/compiler/lib/src/ssa/invoke_dynamic_specializers.dart b/pkg/compiler/lib/src/ssa/invoke_dynamic_specializers.dart
index 51ff1f353ca85b5938b0144e65fbf07a3edf2cbc..bf15133d169fd1ff4b750d40de00483af2f87e34 100644
--- a/pkg/compiler/lib/src/ssa/invoke_dynamic_specializers.dart
+++ b/pkg/compiler/lib/src/ssa/invoke_dynamic_specializers.dart
@@ -936,7 +936,7 @@ class EqualsSpecializer extends RelationalSpecializer {
     // implemented because if the selector matches by subtype, it still will be
     // a regular object or an interceptor.
     if (matches
-        .every(closedWorld.backendClasses.isDefaultEqualityImplementation)) {
+        .every(closedWorld.commonElements.isDefaultEqualityImplementation)) {
       return newBuiltinVariant(instruction, closedWorld);
     }
     return null;