Bring in the latest pub.

CHANGELOG.md

 ## 1.16.0
 
 ### Analyzer
 
 *   Static checking of `for in` statements. These will now produce static
     warnings:
 
     ```dart
     // Not Iterable.
     for (var i in 1234) { ... }
 
     // String cannot be assigned to int.
     for (int n in <String>["a", "b"]) { ... }
     ```
 
+### Tool Changes
+
+* Pub
+  * `pub serve` now provides caching headers that should improve the performance
+    of requesting large files multiple times.
+
+  * Both `pub get` and `pub upgrade` now have a `--no-precompile` flag that
+    disables precompilation of executables and transformed dependencies.
+
 ## 1.15.0 - 2016-03-09
 
 ### Core library changes
 
 * `dart:async`
   * Made `StreamView` class a `const` class.
 
 * `dart:core`
   * Added `Uri.queryParametersAll` to handle multiple query parameters with
     the same name.
@@ skipping 831 matching lines @@
     they will keep the Dart process alive until they time out. This fixes the
     handling of persistent connections. Previously, the client would shut down
     immediately after a request.
 
   * **Breaking change:** `HttpServer` no longer compresses all traffic by
     default. The new `autoCompress` property can be set to `true` to re-enable
     compression.
 
 * `dart:isolate`: `Isolate.spawnUri` added the optional `packageRoot` argument,
   which controls how it resolves `package:` URIs.