Add observatory_pub_packages snapshot to third_party

observatory_pub_packages/source_span/src/utils.dart

Index: observatory_pub_packages/source_span/src/utils.dart
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--- observatory_pub_packages/source_span/src/utils.dart	(revision 0)
+++ observatory_pub_packages/source_span/src/utils.dart	(working copy)
@@ -0,0 +1,39 @@
+// 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.
+
+library source_span.utils;
+
+/// Returns the minimum of [obj1] and [obj2] according to
+/// [Comparable.compareTo].
+Comparable min(Comparable obj1, Comparable obj2) =>
+    obj1.compareTo(obj2) > 0 ? obj2 : obj1;
+
+/// Returns the maximum of [obj1] and [obj2] according to
+/// [Comparable.compareTo].
+Comparable max(Comparable obj1, Comparable obj2) =>
+    obj1.compareTo(obj2) > 0 ? obj1 : obj2;
+
+/// Find the first entry in a sorted [list] that matches a monotonic predicate.
+///
+/// Given a result `n`, that all items before `n` will not match, `n` matches,
+/// and all items after `n` match too. The result is -1 when there are no
+/// items, 0 when all items match, and list.length when none does.
+int binarySearch(List list, bool matches(item)) {
+  if (list.length == 0) return -1;
+  if (matches(list.first)) return 0;
+  if (!matches(list.last)) return list.length;
+
+  int min = 0;
+  int max = list.length - 1;
+  while (min < max) {
+    var half = min + ((max - min) ~/ 2);
+    if (matches(list[half])) {
+      max = half;
+    } else {
+      min = half + 1;
+    }
+  }
+  return max;
+}
+