Add missing Cargo.lock deps change.
Mark the append_style reftest as flaky until we get better reliability. Fixes #3805.
Customize RefCell instead of wrapping it

This gets rid of a dubious transmute:

    let val = mem::transmute::<&RefCell<T>, &T>(&self.base);

The code duplication will be reduced once rust-lang/rust#18131 is fixed.
Fix a layout method to use borrow_for_layout()
Dynamically check DOMRefCell access from layout in debug builds
Ignore the HTML parser's borrow flag in GC tracing

Adds some other dynamic checks in debug builds.
task_state: Generate the list of task types

Also fix warnings.
Provide safety check helpers in release builds

debug_assert! uses

    if cfg!(not(ndebug)) { ... }

so the body in a release build is dead code, but it still needs to compile.
Implement [LenientThis] support and enable it in Document.webidl

Closes issue #3760
Add content test for [LenientThis] attribute Document.onreadystatechange
Disable Document interface attribute onreadystatechange test

idlharness.js does not understand [LenientThis] yet
added ErrorEvent WebIDL and errorevent.rs

JSVal issue

ErrorEvent compile time errors resolution # 1

getter and setter errors

DOMString error resolved

removed tabs, trailing whitespace, added licence

prettification

fixes based on code review

changes as per code review v1

revisions: indentations issues, removed extraneous  attributes

indentation

Added ErrorEvent.WEbIDL and errorevent.rs
Merge remote-tracking branch 'ronak/master'