Revive throw as an expression but not for rethrow.

sdk/lib/_internal/compiler/implementation/tree/nodes.dart

 // Copyright (c) 2012, 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.
 
 part of tree;
 
 abstract class Visitor<R> {
   const Visitor();
 
   R visitNode(Node node);
@@ skipping 54 matching lines @@
   R visitSend(Send node) => visitExpression(node);
   R visitSendSet(SendSet node) => visitSend(node);
   R visitStatement(Statement node) => visitNode(node);
   R visitStringNode(StringNode node) => visitExpression(node);
   R visitStringInterpolation(StringInterpolation node) => visitStringNode(node);
   R visitStringInterpolationPart(StringInterpolationPart node) {
     return visitNode(node);
   }
   R visitSwitchCase(SwitchCase node) => visitNode(node);
   R visitSwitchStatement(SwitchStatement node) => visitStatement(node);
-  R visitThrow(Throw node) => visitStatement(node);
+  R visitThrow(Throw node) => visitExpression(node);
   R visitTryStatement(TryStatement node) => visitStatement(node);
   R visitTypeAnnotation(TypeAnnotation node) => visitNode(node);
   R visitTypedef(Typedef node) => visitNode(node);
   R visitTypeVariable(TypeVariable node) => visitNode(node);
   R visitVariableDefinitions(VariableDefinitions node) => visitStatement(node);
   R visitWhile(While node) => visitLoop(node);
 }
 
 Token firstBeginToken(Node first, Node second) {
   Token token = null;
@@ skipping 847 matching lines @@
 
   visitChildren(Visitor visitor) {
     if (expression != null) expression.accept(visitor);
   }
 
   Token getBeginToken() => expression.getBeginToken();
 
   Token getEndToken() => endToken;
 }
 
-class Throw extends Statement {
+class Throw extends Expression {
   final Expression expression;
 
   final Token throwToken;
   final Token endToken;
 
   Throw(this.expression, this.throwToken, this.endToken);
 
   Throw asThrow() => this;
 
   accept(Visitor visitor) => visitor.visitThrow(this);
@@ skipping 1044 matching lines @@
  * argument).
  *
  * TODO(ahe): This method is controversial, the team needs to discuss
  * if top-level methods are acceptable and what naming conventions to
  * use.
  */
 initializerDo(Node node, f(Node node)) {
   SendSet send = node.asSendSet();
   if (send != null) return f(send.arguments.head);
 }