diff --git a/src/com/google/dart/compiler/backend/js/ast/ChameleonJsExpression.java b/src/com/google/dart/compiler/backend/js/ast/ChameleonJsExpression.java
new file mode 100644
index 00000000000..eafa8daad93
--- /dev/null
+++ b/src/com/google/dart/compiler/backend/js/ast/ChameleonJsExpression.java
@@ -0,0 +1,87 @@
+package com.google.dart.compiler.backend.js.ast;
+
+import com.google.dart.compiler.Source;
+import com.google.dart.compiler.common.SourceInfo;
+
+public class ChameleonJsExpression implements JsExpression {
+  private JsExpression expression;
+
+  public void resolve(JsExpression expression) {
+    this.expression = expression;
+  }
+
+  @Override
+  public boolean hasSideEffects() {
+    return expression.hasSideEffects();
+  }
+
+  @Override
+  public boolean isDefinitelyNotNull() {
+    return expression.isDefinitelyNotNull();
+  }
+
+  @Override
+  public boolean isDefinitelyNull() {
+    return expression.isDefinitelyNull();
+  }
+
+  @Override
+  public boolean isLeaf() {
+    return expression.isLeaf();
+  }
+
+  @Override
+  public JsStatement makeStmt() {
+    return expression.makeStmt();
+  }
+
+  @Override
+  public NodeKind getKind() {
+    return expression.getKind();
+  }
+
+  @Override
+  public void traverse(JsVisitor visitor, JsContext context) {
+    expression.traverse(visitor, context);
+  }
+
+  @Override
+  public SourceInfo getSourceInfo() {
+    return expression.getSourceInfo();
+  }
+
+  @Override
+  public void setSourceInfo(SourceInfo info) {
+    expression.setSourceInfo(info);
+  }
+
+  @Override
+  public void setSourceLocation(Source source, int line, int column, int startPosition, int length) {
+    expression.setSourceLocation(source, line, column, startPosition, length);
+  }
+
+  @Override
+  public Source getSource() {
+    return expression.getSource();
+  }
+
+  @Override
+  public int getLine() {
+    return 0;
+  }
+
+  @Override
+  public int getColumn() {
+    return expression.getColumn();
+  }
+
+  @Override
+  public int getStart() {
+    return expression.getStart();
+  }
+
+  @Override
+  public int getLength() {
+    return expression.getLength();
+  }
+}
diff --git a/src/com/google/dart/compiler/backend/js/ast/JsDocComment.java b/src/com/google/dart/compiler/backend/js/ast/JsDocComment.java
index ffc8867edae..909fd225846 100644
--- a/src/com/google/dart/compiler/backend/js/ast/JsDocComment.java
+++ b/src/com/google/dart/compiler/backend/js/ast/JsDocComment.java
@@ -3,7 +3,7 @@ package com.google.dart.compiler.backend.js.ast;
 import java.util.Collections;
 import java.util.Map;
 
-public class JsDocComment extends JsExpressionImpl implements JsExpression {
+public class JsDocComment extends JsExpressionImpl {
     private final Map<String, Object> tags;
 
     public JsDocComment(Map<String, Object> tags) {