Add summit demos.

summit2.html is a two pane demo of rust logo and matrix math.

summit3.html is a three pane demo adding longcat.

summit-fail.html is thw two pane demo with failing page on the right.
auto merge of #1011 : metajack/servo/summit-demos, r=larsbergstrom

summit2.html is a two pane demo of rust logo and matrix math.

summit3.html is a three pane demo adding longcat.

summit-fail.html is thw two pane demo with failing page on the right.
Use str.char_offset_iter instead of manually calling str.char_range_at.
Don't require passing a root element to Document::new (needed for issue #888).
Move the User-Agent styleesheet to a CSS file instead of a Rust string.

… as suggested in
https://github.com/mozilla/servo/pull/1015#issuecomment-25755957

Also add a comment on the `border-width` work-around.
auto merge of #1017 : SimonSapin/servo/external-UA-css, r=jdm

… as suggested in https://github.com/mozilla/servo/pull/1015#issuecomment-25755957

Also add a comment on the `border-width` work-around.
Address review comments.
Remove unnecessary mutability.
Fix UA stylesheet: remove Rust string escaping
auto merge of #1020 : SimonSapin/servo/external-UA-css, r=jdm

Oops, I broke the UA stylesheet in #1017. The fact that our tests still passed is not a good sign :/
auto merge of #1012 : deokjinkim/servo/glyph_advance_cache, r=ILyoan

#1008 has unnecessary code change. So I want to revert this code.
Remove Document::set_root.

All callers have an AbstractDocument, and this makes my life easier later.
Cleanup some code.
auto merge of #1023 : Ms2ger/servo/cleanup, r=jdm
auto merge of #1016 : Ms2ger/servo/ownerdoc, r=jdm
Rename CacheableWrapper to Reflectable.
Rename WrapperCache to Reflector.

I think the abstraction from the raw JSObject is still probably worthwhile for
now.
Rename get_wrappercache() to reflector(). v1

I also updated some variable names in the codegen.
Rename {get,set}_wrapper to {get,set}_jsobject. v1
Rename WrappableDocument stuff.