Remove AsyncError with Expando.

sdk/lib/async/async_error.dart

Index: sdk/lib/async/async_error.dart
diff --git a/sdk/lib/async/async_error.dart b/sdk/lib/async/async_error.dart
index fa90e8779b1042a31981f5ee19ed926be0b36df3..161b9ef4abfd924b1564fa32c5185b1abc7116c5 100644
--- a/sdk/lib/async/async_error.dart
+++ b/sdk/lib/async/async_error.dart
@@ -4,70 +4,14 @@
 
 part of dart.async;
 
-/**
- * Error result of an asynchronous computation.
- */
-class AsyncError {
-  /** The actual error thrown by the computation. */
-  final error;
-  /** Stack trace corresponding to the error, if available. */
-  final Object stackTrace;
-  /** Asynchronous error leading to this error, if error handling fails. */
-  final AsyncError cause;
+final Expando _stackTraceExpando = new Expando("asynchronous error");
 
-  // TODO(lrn): When possible, combine into one constructor with both optional
-  // positional and named arguments.
-  AsyncError(this.error, [this.stackTrace]): cause = null;
-  AsyncError.withCause(this.error, this.stackTrace, this.cause);
-
-  void _writeOn(StringSink buffer) {
-    buffer.write("'");
-    String message;
-    try {
-      message = error.toString();
-    } catch (e) {
-      message = Error.safeToString(error);
-    }
-    buffer.write(message);
-    buffer.write("'\n");
-    if (stackTrace != null) {
-      buffer.write("Stack trace:\n");
-      buffer.writeln(stackTrace.toString());
-    }
-  }
-
-  String toString() {
-    StringBuffer buffer = new StringBuffer();
-    buffer.write("AsyncError: ");
-    _writeOn(buffer);
-    AsyncError cause = this.cause;
-    while (cause != null) {
-      buffer.write("Caused by: ");
-      cause._writeOn(buffer);
-      cause = cause.cause;
-    }
-    return buffer.toString();
-  }
-
-  throwDelayed() {
-    reportError() {
-      print("Uncaught Error: $error");
-      if (stackTrace != null) {
-        print("Stack Trace:\n$stackTrace\n");
-      }
-    }
-
-    try {
-      Timer.run(() {
-        reportError();
-        // TODO(floitsch): we potentially want to call the global error handler
-        // directly so that we can pass the stack trace.
-        throw error;
-      });
-    } catch (e) {
-      // Unfortunately there is not much more we can do...
-      reportError();
-    }
-  }
+void _attachStackTrace(o, st) {
+  if (o == null || o is bool || o is num || o is String) return;
+  _stackTraceExpando[o] = st;
 }
 
+getAttachedStackTrace(o) {
+  if (o == null || o is bool || o is num || o is String) return null;
+  return _stackTraceExpando[o];
+}