Add support for rethrow and start treating throw <expr> as an expression.

sdk/lib/_internal/compiler/implementation/resolution/members.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 resolution;
 
 abstract class TreeElements {
   Element get currentElement;
   Set<Node> get superUses;
 
@@ skipping 2425 matching lines @@
   visitNodeList(NodeList node) {
     for (Link<Node> link = node.nodes; !link.isEmpty; link = link.tail) {
       visit(link.head);
     }
   }
 
   visitOperator(Operator node) {
     unimplemented(node, 'operator');
   }
 
+  visitRethrow(Rethrow node) {
+    if (!inCatchBlock) {
+      error(node, MessageKind.THROW_WITHOUT_EXPRESSION);
+    }
+  }
+
   visitReturn(Return node) {
     if (node.isRedirectingFactoryBody) {
       handleRedirectingFactoryBody(node);
     } else {
       visit(node.expression);
     }
   }
 
   void handleRedirectingFactoryBody(Return node) {
     final isSymbolConstructor = enclosingElement == compiler.symbolConstructor;
@@ skipping 32 matching lines @@
     world.registerInstantiatedClass(
         redirectionTarget.enclosingElement.declaration, mapping);
     if (isSymbolConstructor) {
       // Make sure that collection_dev.Symbol.validated is registered.
       assert(invariant(node, compiler.symbolValidatedConstructor != null));
       world.registerStaticUse(compiler.symbolValidatedConstructor);
     }
   }
 
   visitThrow(Throw node) {
-    if (!inCatchBlock && node.expression == null) {
-      error(node, MessageKind.THROW_WITHOUT_EXPRESSION);
-    }
-    // We don't know ahead of time whether we will need the throw in a statement
-    // context or an expression context, so we register both here, even though
-    // we may not need ThrowExpression.
+    // We don't know ahead of time whether we will need the throw in a
+    // statement context or an expression context, so we register both
+    // here, even though we may not need ThrowExpression.
     compiler.backend.registerWrapException(mapping);
     compiler.backend.registerThrowExpression(mapping);
     visit(node.expression);
   }
 
   visitVariableDefinitions(VariableDefinitions node) {
     VariableDefinitionsVisitor visitor =
         new VariableDefinitionsVisitor(compiler, node, this,
                                        ElementKind.VARIABLE);
     // Ensure that we set the type of the [VariableListElement] since it depends
@@ skipping 1446 matching lines @@
     return e;
   }
 
   /// Assumed to be called by [resolveRedirectingFactory].
   Element visitReturn(Return node) {
     Node expression = node.expression;
     return finishConstructorReference(visit(expression),
                                       expression, expression);
   }
 }