Remove backends.

compiler/java/com/google/dart/compiler/backend/js/ast/JsPrefixOperation.java

-// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-
-package com.google.dart.compiler.backend.js.ast;
-
-/**
- * A JavaScript prefix operation.
- */
-public final class JsPrefixOperation extends JsUnaryOperation implements CanBooleanEval {
-
-  public JsPrefixOperation(JsUnaryOperator op) {
-    this(op, null);
-  }
-
-  public JsPrefixOperation(JsUnaryOperator op, JsExpression arg) {
-    super(op, arg);
-  }
-
-  @Override
-  public boolean isBooleanFalse() {
-    if (getOperator() == JsUnaryOperator.VOID) {
-      return true;
-    }
-    if (getOperator() == JsUnaryOperator.NOT && getArg() instanceof CanBooleanEval) {
-      CanBooleanEval eval = (CanBooleanEval) getArg();
-      return eval.isBooleanTrue();
-    }
-    return false;
-  }
-
-  @Override
-  public boolean isBooleanTrue() {
-    if (getOperator() == JsUnaryOperator.NOT && getArg() instanceof CanBooleanEval) {
-      CanBooleanEval eval = (CanBooleanEval) getArg();
-      return eval.isBooleanFalse();
-    }
-    if (getOperator() == JsUnaryOperator.TYPEOF) {
-      return true;
-    }
-    return false;
-  }
-
-  @Override
-  public boolean isDefinitelyNotNull() {
-    if (getOperator() == JsUnaryOperator.TYPEOF) {
-      return true;
-    }
-    return getOperator() != JsUnaryOperator.VOID;
-  }
-
-  @Override
-  public boolean isDefinitelyNull() {
-    return getOperator() == JsUnaryOperator.VOID;
-  }
-
-  @Override
-  public void traverse(JsVisitor v, JsContext ctx) {
-    if (v.visit(this, ctx)) {
-      super.traverse(v, ctx);
-    }
-    v.endVisit(this, ctx);
-  }
-
-  @Override
-  public NodeKind getKind() {
-    return NodeKind.PREFIX_OP;
-  }
-}