layout: Support more types of selectors for style sharing.

This helps avoid problems with style sharing in common cases, often
caused by the user agent stylesheet.
Disable indexed-browsing-contexts-01.html for flakiness.
auto merge of #3848 : Ms2ger/servo/indexed, r=mbrubeck
Infrastructure for synchronous script loading

This implements the parts of the "prepare a script element" algorithm that are
required for synchronous scripts.  It also adds some infrastructure for future
support of the `async` and `defer` attributes.
Switch to synchronous script loading

This removes the old code for asyncronously loading scripts during HTML
parsing and then executing them afterward.

Fixes #3356.
Don't force reflow on content changes

This fixes a performance regression caused by the previous patches.  Once we
allowed script and layout to run during parsing, it was running too often
(every time the document changed and called window.reflow).

Fixes #1269.
Implement cloning steps for script element
Test for sync script loading
auto merge of #3721 : mbrubeck/servo/script-sync, r=Ms2ger

Fixes #3356.  This makes script elements fetch their source synchronously and execute immediately by default.  It also lays some groundwork for future deferred or async script loading.

(Depends on #3716 to fix a content test failure caused by running script during parsing.)
Update to use new GL bindings.
auto merge of #3851 : glennw/servo/servo_gl, r=glennw,metajack
Format Element#tagName correctly when there's a prefix.

format!("{}", atom) yields strings like "Atom('span' type=Inline)", which is
not intended here.
Move build_element_from_tag out of the HTML parser.

This function is not particular to the parser, so should live in the DOM.
auto merge of #3853 : Ms2ger/servo/create, r=Manishearth

This function is not particular to the parser, so should live in the DOM.
auto merge of #3856 : Ms2ger/servo/tagname, r=Manishearth

format!("{}", atom) yields strings like "Atom('span' type=Inline)", which is
not intended here.
Cleanup Element's AttributeHandlers

Remove notify_attribute_{changed,removed} in favor of a unified
notify_content_changed.
auto merge of #3859 : brunoabinader/servo/element-notify-content-changed, r=Ms2ger

Remove ```notify_attribute_{changed,removed}``` in favor of a unified ```notify_content_changed```. In the future, whether we decide to specialize ```document.content_changed()```, it'll be just a matter of adding a param.
Update azure. This removes the final rust-opengles dependency.
auto merge of #3861 : glennw/servo/update-azure, r=metajack
auto merge of #3838 : pcwalton/servo/style-sharing-enhancements, r=SimonSapin

This helps avoid problems with style sharing in common cases, often
caused by the user agent stylesheet.

r? @SimonSapin