Implement Document.readyState. Prevent iframes from notifying the compositor after the initial parse. Fixes #1720. Fixes #3738.
auto merge of #3759 : jdm/servo/readystate, r=Ms2ger

...itor after the initial parse. Fixes #1720. Fixes #3738.

r? @Ms2ger or @Manishearth
layout: Shrink fragments down from 448 bytes down to 128 bytes.

16% performance improvement in layout (!)
Cleanup some Document methods.
Introduce LayoutDocumentHelpers::is_html_document_for_layout for LayoutElementHelpers::html_element_in_html_document_for_layout.
Move the methods on bare Document onto DocumentHelpers.
Cleanup Document::Title.
embedding: fix string_list deallocation where I accidentally the whole string_list
auto merge of #3780 : Ms2ger/servo/cleanup-document, r=jdm
embedding: fix string_list compile errors?
embedding: add string_map_to_vec() to reduce transmute calls
auto merge of #3772 : pcwalton/servo/slim-down-fragment, r=metajack

16% performance improvement in layout (!)

r? @metajack (or whoever)
auto merge of #3785 : zmike/servo/embedding-fixups-for-string_list, r=larsbergstrom

r+ @jdm @larsbergstrom  ?
Update style/README.md - libcss is gone now
Cache last fontgroup. Style recalc on wikipedia/rust 66ms -> 41ms.
Fix build warnings in the cef port.
Make some warnings errors in the cef port.
Really fix #3738 by only processing iframe src attributes during parsing.
auto merge of #3782 : Ms2ger/servo/cef-warnings, r=Ms2ger,metajack
Add layers dependency to util crate. Fixes #3783.