Replace Backend with JavaScriptBackend.

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

Index: pkg/compiler/lib/src/ssa/builder_kernel.dart
diff --git a/pkg/compiler/lib/src/ssa/builder_kernel.dart b/pkg/compiler/lib/src/ssa/builder_kernel.dart
index 9bbc96dfb3388d5204af7d8495b8d6449ee49b1b..ae268dadd2613c4dc243f0a02bd8e44eee840b1e 100644
--- a/pkg/compiler/lib/src/ssa/builder_kernel.dart
+++ b/pkg/compiler/lib/src/ssa/builder_kernel.dart
@@ -814,7 +814,7 @@ class KernelSsaBuilder extends ir.Visitor with GraphBuilder {
       Local loopVariableLocal = astAdapter.getLocal(forInStatement.variable);
       localsHandler.updateLocal(loopVariableLocal, value);
       // Hint to name loop value after name of loop variable.
-      if (loopVariableLocal is !SyntheticLocal) {
+      if (loopVariableLocal is! SyntheticLocal) {
         value.sourceElement ??= loopVariableLocal;
       }
 
@@ -876,7 +876,7 @@ class KernelSsaBuilder extends ir.Visitor with GraphBuilder {
       HInstruction value = pop();
       localsHandler.updateLocal(loopVariableLocal, value);
       // Hint to name loop value after name of loop variable.
-      if (loopVariableLocal is !SyntheticLocal) {
+      if (loopVariableLocal is! SyntheticLocal) {
         value.sourceElement ??= loopVariableLocal;
       }
       forInStatement.body.accept(this);