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

CHANGELOG.md

 ## 1.25.0
 
 ### Language
 * A string in a `part of` declaration may now be used to refer to the library
   this file is part of.
   A library part can now declare its library either as:
   `part of name.of.library;` or as `part of "uriReferenceOfLibrary.dart";`.
   This allows libraries with no library declarations (and therefore no name)
   to have parts, and it allows tools to easily find the library of a part
   file.
@@ skipping 55 matching lines @@
     time (in ms) to wait between file watcher events before scheduling a build.
     Defaults to 50.
 
   * Removed require.js module loading timeout for dartdevc, which resolves an
     issue where the initial load of an app might give a timeout error.
 
 * dartfmt
 
     * Support assert in const constructor initializer lists.
     * Better formatting for multi-line strings in argument lists.
+    wasn't in a Git repository.
+
+* Dart Dev Compiler
+
+  * dartdevc will no longer throw an error from `is` checks that return a
+    different result in weak mode
+    (SDK issue [28988](https://github.com/dart-lang/sdk/issues/28988)).
+    For example:
+    ```dart
+    main() {
+      List l = [];
+      // Prints "false", does not throw.
+      print(l is List<String>);
+    }
+    ```
 
 ## 1.24.2 - 22-06-2017
 
 * Fixes for debugging in Dartium.
   * Fix DevConsole crash with JS
       (https://github.com/dart-lang/sdk/issues/29873).
   * Fix debugging in WebStorm, NULL returned for JS objects
       (https://github.com/dart-lang/sdk/issues/29854).
 
 ## 1.24.1 - 14-06-2017
@@ skipping 2081 matching lines @@
     they will keep the Dart process alive until they time out. This fixes the
     handling of persistent connections. Previously, the client would shut down
     immediately after a request.
 
   * **Breaking change:** `HttpServer` no longer compresses all traffic by
     default. The new `autoCompress` property can be set to `true` to re-enable
     compression.
 
 * `dart:isolate`: `Isolate.spawnUri` added the optional `packageRoot` argument,
   which controls how it resolves `package:` URIs.