Move _fatal to dart:async

runtime/lib/async_patch.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.
 
 import "dart:_internal";
 
+// Equivalent of calling FATAL from C++ code.
+_fatal(msg) native "DartAsync_fatal";
+
 // We need to pass the value as first argument and leave the second and third
 // arguments empty (used for error handling).
 // See vm/ast_transformer.cc for usage.
 Function _asyncThenWrapperHelper(continuation) {
   // Any function that is used as an asynchronous callback must be registered
   // in the current Zone. Normally, this is done by the future when a
   // callback is registered (for example with `.then` or `.catchError`). In our
   // case we want to reuse the same callback multiple times and therefore avoid
   // the multiple registrations. For our internal futures (`_Future`) we can
   // use the shortcut-version of `.then`, and skip the registration. However,
@@ skipping 73 matching lines @@
   // execution of the generator.
   //
   // TODO(hausner): Per spec, the generator should be suspended before
   // exiting when the stream is closed. We could add a getter like this:
   // get isCancelled => controller.hasListener;
   // The generator would translate a 'yield e' statement to
   // controller.add(e);
   // suspend;
   // if (controller.isCancelled) return;
   bool add(event) {
-    if (!onListenReceived) fatal("yield before stream is listened to!");
-    if (isSuspendedAtYield) fatal("unexpected yield");
+    if (!onListenReceived) _fatal("yield before stream is listened to");
+    if (isSuspendedAtYield) _fatal("unexpected yield");
     // If stream is cancelled, tell caller to exit the async generator.
     if (!controller.hasListener) {
       return true;
     }
     controller.add(event);
     scheduleGenerator();
     isSuspendedAtYield = true;
     return false;
   }
 
   // Adds the elements of stream into this controller's stream.
   // The generator will be scheduled again when all of the
   // elements of the added stream have been consumed.
   // Returns true if the caller should terminate
   // execution of the generator.
   bool addStream(Stream stream) {
-    if (!onListenReceived) fatal("yield before stream is listened to!");
+    if (!onListenReceived) _fatal("yield before stream is listened to");
     // If stream is cancelled, tell caller to exit the async generator.
     if (!controller.hasListener) return true;
     isAdding = true;
     var whenDoneAdding =
         controller.addStream(stream as Stream, cancelOnError: false);
     whenDoneAdding.then((_) {
       isAdding = false;
       scheduleGenerator();
       if (!isScheduled) isSuspendedAtYield = true;
     });
@@ skipping 65 matching lines @@
 
 /// Returns a [StackTrace] object containing the synchronous prefix for this
 /// asynchronous method.
 Object _asyncStackTraceHelper() native "StackTrace_asyncStackTraceHelper";
 
 void _clearAsyncThreadStackTrace()
     native "StackTrace_clearAsyncThreadStackTrace";
 
 void _setAsyncThreadStackTrace(StackTrace stackTrace) native
     "StackTrace_setAsyncThreadStackTrace";