In order to tailor certain security checks to the caller that is
attempting to load a particular piece of content, we need to be able to
attach an appropriate triggering principal to the corresponding requests.
Since most HTML content is loaded based on attribute values, this means
capturing the subject principal of the caller who sets those attributes,
which in turn means we need to make it available to `AfterSetAttr` hooks
on all relevant element types.
This removes a lot of the plumbing for having the platform embed itself
through IPC which was required for B2G running the browser as both
shell and browser application.
* Remove the generic attr preparsing mechanism from BeforeSetAttr and just preparse class attributes directly in the one place that needs to do it
* Move calls to BeforeSetAttr to after AttributeWillChange
* Remove UpdateState calls in BeforeSetAttr
* Move calls to AfterSetAttr to before UpdateState when manipulating attributes
* Remove UpdateState calls from AfterSetAttr, since they are no longer needed there
Tag #1375
* Rename nsIDOMEventTarget::PreHandleEvent to nsIDOMEventTarget::GetEventTargetParent
* Add nsIDOMEventTarget::PreHandleEvent
* Add EventTargetChainItem::GetFirstEventTarget
* Call EventTargetChainItem::PreHandleEvent even it sets mCanHandle=false
* Move form control frame focus/blur from nsGenericHTMLFormElement::GetEventTargetParent to PreHandleEvent
* Move fire change event from HTMLTextAreaElement::GetEventTargetParent to PreHandleEvent
* Refine nsXULElement::GetEventTargetParent
* Move dispatch XUL command from nsXULElement::GetEventTargetParent to PreHandleEvent
* Move fire events and set value from HTMLInputElement::GetEventTargetParent to PreHandleEvent
* Add test case
* Let HTMLInputElement delegate event handling to it's parent class
* Refine EventTargetChain flags to reduce overheads
* Refine event target chain creation
* Refine assertion in EventTargetChainItem::Create
Tag #1375
