Use failedAt in more places (js_emitter)

pkg/compiler/lib/src/js_emitter/native_emitter.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.
 
 library dart2js.js_emitter.native_emitter;
 
 import '../common.dart';
 import '../common_elements.dart' show CommonElements;
 import '../elements/types.dart' show DartType, FunctionType;
 import '../elements/entities.dart';
@@ skipping 293 matching lines @@
     // must be turned into a JS call to:
     //   foo(null, y).
 
     List<jsAst.Statement> statements = <jsAst.Statement>[];
     potentiallyConvertDartClosuresToJs(statements, member, stubParameters);
 
     String target;
     jsAst.Expression receiver;
     List<jsAst.Expression> arguments;
 
-    assert(invariant(member, nativeMethods.contains(member)));
+    assert(nativeMethods.contains(member), failedAt(member));
     // When calling a JS method, we call it with the native name, and only the
     // arguments up until the last one provided.
     target = _nativeData.getFixedBackendName(member);
 
     if (isInterceptedMethod) {
       receiver = argumentsBuffer[0];
       arguments = argumentsBuffer.sublist(
           1, indexOfLastOptionalArgumentInParameters + 1);
     } else {
       // Native methods that are not intercepted must be static.
-      assert(invariant(member, member.isStatic));
+      assert(member.isStatic, failedAt(member));
       arguments = argumentsBuffer.sublist(
           0, indexOfLastOptionalArgumentInParameters + 1);
       if (_nativeData.isJsInteropMember(member)) {
         // fixedBackendPath is allowed to have the form foo.bar.baz for
         // interop. This template is uncached to avoid possibly running out of
         // memory when Dart2Js is run in server mode. In reality the risk of
         // caching these templates causing an issue  is very low as each class
         // and library that uses typed JavaScript interop will create only 1
         // unique template.
         receiver = js
@@ skipping 23 matching lines @@
     // satisfy a check against [element], in which case an interceptor must be
     // used.  We should also use an interceptor if the check can't be satisfied
     // by a native class in case we get a native instance that tries to spoof
     // the type info.  i.e the criteria for whether or not to use an interceptor
     // is whether the receiver can be native, not the type of the test.
     ClassEntity cls = element;
     if (_nativeData.isNativeOrExtendsNative(cls)) return true;
     return isSupertypeOfNativeClass(element);
   }
 }