Emit classes using ASTs

sdk/lib/_internal/compiler/implementation/js_backend/backend.dart

Index: sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
diff --git a/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart b/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
index 463d2a716b27310fed1ed216b67b0e1b6f996eae..e2c13472d37fa3771b0659581f297ec1a56d0beb 100644
--- a/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
+++ b/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
@@ -917,13 +917,13 @@ class JavaScriptBackend extends Backend {
     optimizer.optimize(work, graph, false);
     if (work.allowSpeculativeOptimization
         && optimizer.trySpeculativeOptimizations(work, graph)) {
-      CodeBuffer codeBuffer = generator.generateBailoutMethod(work, graph);
-      compiler.codegenWorld.addBailoutCode(work, codeBuffer);
+      js.Expression code = generator.generateBailoutMethod(work, graph);
+      compiler.codegenWorld.addBailoutCode(work, code);
       optimizer.prepareForSpeculativeOptimizations(work, graph);
       optimizer.optimize(work, graph, true);
     }
-    CodeBuffer codeBuffer = generator.generateCode(work, graph);
-    compiler.codegenWorld.addGeneratedCode(work, codeBuffer);
+    js.Expression code = generator.generateCode(work, graph);
+    compiler.codegenWorld.addGeneratedCode(work, code);
     invalidateAfterCodegen.forEach(compiler.enqueuer.codegen.eagerRecompile);
     invalidateAfterCodegen.clear();
   }