Make sure RefCell borrows are temporary.

This fixes two `RefCell<T> is already borrowed` failures when reloading an
existing pipeline, both caused by functions trying to modify `Pipeline::url`
or `ScriptTask::url` while a reference to a previous borrow is still in scope.
Remove unused invalidate_rect code
Update expectations.
auto merge of #2211 : Ms2ger/servo/update-expectation, r=Ms2ger
auto merge of #2208 : mbrubeck/servo/dead-invalidate-rect, r=metajack

This is dead code; should we remove it, or are there plans to use it sometime soon?

r? @pcwalton
auto merge of #2203 : mbrubeck/servo/back-crash, r=jdm

This fixes two `RefCell<T> is already borrowed` failures when reloading an
existing pipeline, both caused by functions trying to modify `Pipeline::url`
or `ScriptTask::url` while a reference to a previous borrow is still in scope.

Note: After applying this patch, there are some painting issues after navigating back.
Make the I Tried star appear when a top-level page load fails for network-related reasons.

Under the hood, this requires treating the I Tried pipeline as a new load instead of a replacement, since the failure-handling code interacts poorly with the rest of the replacement code when we get a series of staggered failures over time from the various pipeline components.
auto merge of #2200 : jdm/servo/loadfail, r=mbrubeck

...k-related reasons.

Under the hood, this requires treating the I Tried pipeline as a new load instead of a replacement, since the failure-handling code interacts poorly with the rest of the replacement code when we get a series of staggered failures over time from the various pipeline components.
Add NodeHelpers::get_bounding_content_box().
Add NodeHelpers::get_content_boxes().
Add Page::hit_test().
Add Page::get_nodes_under_mouse().
auto merge of #2210 : saneyuki/servo/query, r=jdm

- see #356
- To decrease the conversion code, `JS<Node>` -> `Node`, I added API methods to `NodeHelpers`.
- I added APIs to `Page` not `Document` because I had thought that their APIs returns the hitted nodes address in the "page".