* Cleanup a bit the ShadowRoot code
* Privatize ShadowRoot methods
* When the shadow tree distribution changes, post a restyle + reframe
* Simplify ShadowRoot::IsPooledNode
* Be a bit better at detecting distribution changes
Tag #1375
* Moves side effects of nsGenericHTMLElement and Element's SetAttr, UnsetAttr, and ParseAttribute functions to the corresponding BeforeSetAttr and AfterSetAttr functions
* Moves side effects of HTMLAnchorElement's SetAttr, UnsetAttr, and ParseAttribute functions to the corresponding BeforeSetAttr and AfterSetAttr functions
* Moves side effects of HTMLImageElement's SetAttr function to the corresponding BeforeSetAttr and AfterSetAttr functions
* Moves side effects of SetAttr, UnsetAttr, and ParseAttribute functions to BeforeSetAttr and AfterSetAttr
Tag #1375