dart2js cps: Support async/await by rewriting the JavaScript AST.

pkg/compiler/lib/src/cps_ir/cps_ir_builder_task.dart

 // Copyright (c) 2013, 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.
 
 library dart2js.ir_builder_task;
 
 import '../closure.dart' as closurelib;
 import '../closure.dart' hide ClosureScope;
 import '../constants/expressions.dart';
 import '../dart_types.dart';
@@ skipping 335 matching lines @@
         buildBody: subbuild(node.body),
         target: elements.getTargetDefinition(node),
         closureScope: getClosureScopeForNode(node));
   }
 
   visitAsyncForIn(ast.AsyncForIn node) {
     // await for is not yet implemented.
     return giveup(node, 'await for');
   }
 
+  visitAwait(ast.Await node) {
+    ir.Primitive value = visit(node.expression);
+    return irBuilder.buildAwait(value);
+  }
+
   visitSyncForIn(ast.SyncForIn node) {
     // [node.declaredIdentifier] can be either an [ast.VariableDefinitions]
     // (defining a new local variable) or a send designating some existing
     // variable.
     ast.Node identifier = node.declaredIdentifier;
     ast.VariableDefinitions variableDeclaration =
         identifier.asVariableDefinitions();
     Element variableElement = elements.getForInVariable(node);
     Selector selector = elements.getSelector(identifier);
 
@@ skipping 1805 matching lines @@
           tryNestingStack[i + 1].boxedOnEntry.add(local);
         }
       }
     }
     node.visitChildren(this);
   }
 
   visitFunctionExpression(ast.FunctionExpression node) {
     FunctionElement oldFunction = currentFunction;
     currentFunction = elements[node];
-    if (currentFunction.asyncMarker != AsyncMarker.SYNC) {
-      giveup(node, "cannot handle async/sync*/async* functions");
+
+    if (currentFunction.asyncMarker != AsyncMarker.SYNC &&
+        currentFunction.asyncMarker != AsyncMarker.ASYNC) {
+      giveup(node, "cannot handle sync*/async* functions");
     }
+
     if (node.initializers != null) {
       insideInitializer = true;
       visit(node.initializers);
       insideInitializer = false;
     }
     visit(node.body);
     currentFunction = oldFunction;
   }
 
   visitTryStatement(ast.TryStatement node) {
@@ skipping 1141 matching lines @@
     if (compiler.backend.isForeign(function)) {
       return handleForeignCode(node, function, argumentList, callStructure);
     } else {
       return irBuilder.buildStaticFunctionInvocation(function, callStructure,
           translateStaticArguments(argumentList, function, callStructure),
           sourceInformation:
               sourceInformationBuilder.buildCall(node, node.selector));
     }
   }
 }