Add optional message to assert in Dart2js.

pkg/compiler/lib/src/dart_backend/placeholder_collector.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 dart_backend;
 
 class LocalPlaceholder {
   final String identifier;
   final Set<Node> nodes;
   LocalPlaceholder(this.identifier) : nodes = new Set<Node>();
@@ skipping 27 matching lines @@
 }
 
 class SendVisitor extends Visitor {
   final TreeElements elements;
   final PlaceholderCollector collector;
 
   SendVisitor(this.collector, this.elements);
 
   visitSend(Send node) {
     Element element = elements[node];
-    if (elements.isAssert(node)) {
-      return;
-    } else if (elements.isTypeLiteral(node)) {
+    if (elements.isTypeLiteral(node)) {
       DartType type = elements.getTypeLiteralType(node);
       if (!type.isDynamic) {
         if (type is TypeVariableType) {
           collector.makeTypeVariablePlaceholder(node.selector, type);
         } else {
           collector.makeTypePlaceholder(node.selector, type);
         }
       }
     } else if (node.isSuperCall) {
       if (element != null && element.isConstructor) {
@@ skipping 71 matching lines @@
       }
     }
   }
 
   visitStaticSend(Send node) {
     Element element = elements[node];
     collector.mirrorRenamer.registerStaticSend(
         collector.currentElement, element, node);
 
     if (Elements.isUnresolved(element)
-        || elements.isAssert(node)
         || element.isDeferredLoaderGetter) {
       return;
     }
     if (element.isConstructor || element.isFactoryConstructor) {
       // Rename named constructor in redirection position:
       // class C { C.named(); C.redirecting() : this.named(); }
       if (node.receiver is Identifier
           && node.receiver.asIdentifier().isThis()) {
         assert(node.selector is Identifier);
         collector.tryMakeConstructorPlaceholder(node, element);
@@ skipping 564 matching lines @@
 
   visitBlock(Block node) {
     for (Node statement in node.statements.nodes) {
       if (statement is VariableDefinitions) {
         makeVarDeclarationTypePlaceholder(statement);
       }
     }
     node.visitChildren(this);
   }
 }