Expose the exceptions info in the diagnostics page.

pkg/analysis_server/lib/src/collections.dart

Index: pkg/analysis_server/lib/src/collections.dart
diff --git a/pkg/analysis_server/lib/src/collections.dart b/pkg/analysis_server/lib/src/collections.dart
index e89350e41d622f650f9965780142c4a6a078c616..aa635d37361c288c1e2a599f28e4bbcec753c03f 100644
--- a/pkg/analysis_server/lib/src/collections.dart
+++ b/pkg/analysis_server/lib/src/collections.dart
@@ -45,3 +45,27 @@ class Pair<E, F> {
 
   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;
+}