Let the CPS ir builder bail out when given a non-sync function.

pkg/compiler/lib/src/cps_ir/cps_ir_builder_visitor.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.
 
 part of dart2js.ir_builder;
 
 /**
  * This task iterates through all resolved elements and builds [ir.Node]s. The
  * nodes are stored in the [nodes] map and accessible through [hasIr] and
  * [getIr].
@@ skipping 1017 matching lines @@
       // they are captured by a closure (i.e., they do outlive the activation of
       // the function).
       markAsCaptured(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 (node.initializers != null) {
       insideInitializer = true;
       visit(node.initializers);
       insideInitializer = false;
     }
     visit(node.body);
     currentFunction = oldFunction;
   }
 }
 
@@ skipping 73 matching lines @@
         ast.SendSet sendSet = fieldDefinition;
         initializer = visit(sendSet.arguments.first);
       }
       return builder.makeFieldDefinition(initializer);
     });
   }
 
   ir.FunctionDefinition buildFunction(FunctionElement element) {
     assert(invariant(element, element.isImplementation));
     ast.FunctionExpression node = element.node;
+    if (element.asyncMarker != AsyncMarker.SYNC) {
+      giveup(null, 'cannot handle async-await');
+    }
 
     if (!element.isSynthesized) {
       assert(node != null);
       assert(elements[node] != null);
     } else {
       SynthesizedConstructorElementX constructor = element;
       if (!constructor.isDefaultConstructor) {
         giveup(null, 'cannot handle synthetic forwarding constructors');
       }
     }
@@ skipping 536 matching lines @@
     for (String argName in selector.getOrderedNamedArguments()) {
       int nameIndex = selector.namedArguments.indexOf(argName);
       int translatedIndex = selector.positionalArgumentCount + nameIndex;
       result.add(arguments[translatedIndex]);
     }
     return result;
   }
 
 }