Use index in J/KTypeVariable and fix remaining inequivalence

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

Index: pkg/compiler/lib/src/ssa/builder.dart
diff --git a/pkg/compiler/lib/src/ssa/builder.dart b/pkg/compiler/lib/src/ssa/builder.dart
index ff49942f217fafc05b58505b801a8c4e9734ec5c..dd05282875977cb0ad12584d76103f9cb001e98d 100644
--- a/pkg/compiler/lib/src/ssa/builder.dart
+++ b/pkg/compiler/lib/src/ssa/builder.dart
@@ -727,7 +727,7 @@ class SsaAstGraphBuilder extends ast.Visitor
     // the beginning of the method. This is to avoid having call sites do the
     // null check.
     if (name == '==') {
-      if (!backend.operatorEqHandlesNullArgument(functionElement)) {
+      if (!commonElements.operatorEqHandlesNullArgument(functionElement)) {
         handleIf(
             node: function,
             visitCondition: () {