Expose the exceptions info in the diagnostics page.

pkg/analysis_server/lib/src/collections.dart

 // Copyright (c) 2014, 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.
 
 /**
  * Returns the concatenation of the input [iterables].
  *
  * The returned iterable is a lazily-evaluated view on the input iterables.
  */
 Iterable/*<E>*/ concat/*<E>*/(Iterable<Iterable/*<E>*/ > iterables) =>
@@ skipping 27 matching lines @@
 
   int get hashCode => first.hashCode ^ last.hashCode;
 
   bool operator ==(other) {
     if (other is! Pair) return false;
     return other.first == first && other.last == last;
   }
 
   String toString() => '($first, $last)';
 }
+
+/**
+ * A container that remembers the last `n` items added to it.
+ *
+ * It will never grow larger than [capacity]. It's a LIFO queue - the last item
+ * added will be the first one returned from [items].
+ */
+class RecentBuffer<T> {
+  final int capacity;
+
+  List<T> _buffer = [];
+
+  RecentBuffer(this.capacity);
+
+  void add(T item) {
+    _buffer.add(item);
+
+    if (_buffer.length > capacity) {
+      _buffer.removeAt(0);
+    }
+  }
+
+  Iterable<T> get items => _buffer.reversed;
+}