Persist size of outline view on resizing

@devoncarew: This is asymmetrical with the split view because the corresponding markup is asymmetrical. I'm planning to try again to move the chunk with the outline and its resizing splitter from spark_polymer.html to spark_polymer_ui.html: then the symmetry will be restored.

Also removed an unused method.
This use of method cascades (while correct) reads a bit odd to me. I think it would be easier to parse as two separate statements, or with the cascades on separate lines.
```
outlineResizer
  ..targetSize = value
  ..deliverChanges();
```