Added a test for the iframe element sandbox attribute, allow-script
[TTWF Shanghai] Added idlharness test for FileAPI
Update FileAPI IDL to latest editor's draft
Add some cases for the embed element

Signed-off-by: xiaojunwu <xiaojunx.a.wu@intel.com>
Refine tests for the embed element

- Add _manual suffix to reftest filename
- Add a reference file embed_represent_nothing_ref.html
- Remove embed_pass_parameters.html and embed_type_unmatch.html
  as not good design
Custom elements, initial check-in. Custom elements type tests.
Removed incorrect tests for the first combining and ideographic chars
Added tests for letter and digit
Instantiating custom elements tests
Extensions to Document Interface tests
Update according to the new template

1. Update the code format
2. Update the reference specification

Signed-off-by: xiaojunwu <xiaojunx.a.wu@intel.com>
Add test for the URLs resolving
Update idlharness tests to reflect #388 cleanup
Add tests to check resolving URLs in xhtml document
Move tests to web-platform-tests/url directory
Update last patch to remove the files under html/~
Changes according Dominic's review notes:
- xfoo and XFoo replaced by more informative names
- generate_tests replaced by loops
- use assert-throws
- code formatting
Creating and passing registries tests
Template test fixed
Changes according Dominic's review notes:
- use assert_unreached
- for() loops replaced by .forEach()
- more informative variables naming
- code formatting
- tests for template element registry removed
Custom elements lificycle tests