Roll polymer packages to version 0.3.4

pkg/observe/CHANGELOG.md

 # changelog
 
 This file contains highlights of what changes on each version of the observe
 package.
 
+#### Pub version 0.12.0-dev
+  * Updated to match [observe-js#e212e74][e212e74] (release 0.3.4)
+  * ListPathObserver has been deprecated  (it was deleted a while ago in
+    observe-js). We plan to delete it in a future release. You may copy the code
+    if you still need it.
+  * PropertyPath now uses an expression syntax including indexers. For example,
+    you can write `a.b["m"]` instead of `a.b.m`.
+  * **breaking change**: PropertyPath no longer allows numbers as fields, you
+    need to use indexers instead. For example, you now need to write `a[3].d`
+    instead of `a.3.d`.
+
 #### Pub version 0.11.0-dev
   * PathObserver.value= no longer discards changes (this is in combination with
     a change in template_binding and polymer to improve interop with JS custom
     elements).
 
 #### Pub version 0.10.0+3
   * minor changes to documentation, deprecated `discardListChages` in favor of
     `discardListChanges` (the former had a typo).
 
 #### Pub version 0.10.0
   * package:observe no longer declares @MirrorsUsed. The package uses mirrors
     for development time, but assumes frameworks (like polymer) and apps that
     use it directly will either generate code that replaces the use of mirrors,
     or add the @MirrorsUsed declaration themselves. For convinience, you can
     import 'package:observe/mirrors_used.dart', and that will add a @MirrorsUsed
     annotation that preserves properties and classes labeled with @reflectable
     and properties labeled with @observable.
+  * Updated to match [observe-js#0152d54][0152d54]
+
+[0152d54]: https://github.com/Polymer/observe-js/blob/0152d542350239563d0f2cad39d22d3254bd6c2a/src/observe.js
+[e212e74]: https://github.com/Polymer/observe-js/blob/e212e7473962067c099a3d1859595c2f8baa36d7/src/observe.js