fix #28988, remove throw on Dart1 incompatible is-checks for dartdevc

pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/errors.dart

 // Copyright (c) 2015, 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._runtime;
 
 // We need to set these properties while the sdk is only partially initialized
 // so we cannot use regular Dart fields.
 // The default values for these properties are set when the global_ final field
 // in runtime.dart is initialized.
 
 // Override, e.g., for testing
 void trapRuntimeErrors(bool flag) {
   JS('', 'dart.__trapRuntimeErrors = #', flag);
 }
 
 void ignoreWhitelistedErrors(bool flag) {
   JS('', 'dart.__ignoreWhitelistedErrors = #', flag);
 }
 
 void ignoreAllErrors(bool flag) {
   JS('', 'dart.__ignoreAllErrors = #', flag);
 }
 
-/// Throw an exception on `is` checks that would return an unsound answer in
-/// non-strong mode Dart.
-///
-/// For example `x is List<int>` where `x = <Object>['hello']`.
-///
-/// These checks behave correctly in strong mode (they return false), however,
-/// they will produce a different answer if run on a platform without strong
-/// mode. As a debugging feature, these checks can be configured to throw, to
-/// avoid seeing different behavior between modes.
-///
-/// (There are many other ways that different `is` behavior can be observed,
-/// however, even with this flag. The most obvious is due to lack of reified
-/// generic type parameters. This affects generic functions and methods, as
-/// well as generic types when the type parameter was inferred. Setting this
-/// flag to `true` will not catch these differences in behavior..)
-void failForWeakModeIsChecks(bool flag) {
-  JS('', 'dart.__failForWeakModeIsChecks = #', flag);
-}
-
 throwCastError(object, actual, type) {
   var found = typeName(actual);
   var expected = typeName(type);
   if (JS('bool', 'dart.__trapRuntimeErrors')) JS('', 'debugger');
   throw new CastErrorImplementation(object, found, expected);
 }
 
 throwTypeError(object, actual, type) {
   var found = typeName(actual);
   var expected = typeName(type);
@@ skipping 38 matching lines @@
   throw new NoSuchMethodError(
       null, new Symbol('<Unexpected Null Value>'), null, null, null);
 }
 
 throwNoSuchMethodError(Object receiver, Symbol memberName,
     List positionalArguments, Map<Symbol, dynamic> namedArguments) {
   if (JS('bool', 'dart.__trapRuntimeErrors')) JS('', 'debugger');
   throw new NoSuchMethodError(
       receiver, memberName, positionalArguments, namedArguments);
 }