Use entities in BackendClasses

pkg/compiler/lib/src/inferrer/node_tracer.dart

Index: pkg/compiler/lib/src/inferrer/node_tracer.dart
diff --git a/pkg/compiler/lib/src/inferrer/node_tracer.dart b/pkg/compiler/lib/src/inferrer/node_tracer.dart
index 52617803529eece3a87de9d89771e17b9711e87a..f07e46cd0c74437d1c8c17974401c4e24406308c 100644
--- a/pkg/compiler/lib/src/inferrer/node_tracer.dart
+++ b/pkg/compiler/lib/src/inferrer/node_tracer.dart
@@ -336,8 +336,7 @@ abstract class TracerVisitor implements TypeInformationVisitor {
    */
   bool isParameterOfListAddingMethod(Element element) {
     if (!element.isRegularParameter) return false;
-    if (element.enclosingClass !=
-        compiler.backend.backendClasses.listImplementation) {
+    if (element.enclosingClass != compiler.backend.backendClasses.listClass) {
       return false;
     }
     Element method = element.enclosingElement;
@@ -353,8 +352,7 @@ abstract class TracerVisitor implements TypeInformationVisitor {
    */
   bool isParameterOfMapAddingMethod(Element element) {
     if (!element.isRegularParameter) return false;
-    if (element.enclosingClass !=
-        compiler.backend.backendClasses.mapImplementation) {
+    if (element.enclosingClass != compiler.backend.backendClasses.mapClass) {
       return false;
     }
     Element method = element.enclosingElement;