Specs: Move default layout manager stuff from default styles to getLayoutManager()

sky/specs/dom.md

 Sky DOM APIs
 ============
 
 ```javascript
 
 // DOM
 
 typedef ChildNode (Element or Text);
 typedef ChildArgument (Element or Text or String);
 
@@ skipping 105 matching lines @@
 
 class ShadowRoot : TreeScope {
   constructor (Element host); // O(1) // note that there is no way in the API to use a newly created ShadowRoot
   readonly attribute Element host; // O(1)
 }
 
 class Document : TreeScope {
   constructor (ChildArguments... nodes); // O(N) in number of arguments plus all their descendants
 
   virtual LayoutManagerConstructor getLayoutManager(); // O(1)
-    // default implementation returns sky.rootLayoutManager;
+    // returns sky.rootLayoutManager;
 }
 
 attribute LayoutManagerConstructor rootLayoutManager; // O(1)
   // initially configured to return BlockLayoutManager
 
 
 // BUILT-IN ELEMENTS
 
 class ImportElement : Element {
   constructor (Dictionary<String> attributes, ChildArguments... nodes); // O(M+N), M = number of attributes, N = number of nodes plus all their descendants
   constructor (ChildArguments... nodes); // shorthand
   constructor (Dictionary<String> attributes); // shorthand
   constructor (); // shorthand
   constructor attribute String tagName; // O(1) // "import"
   constructor attribute Boolean shadow; // O(1) // false
+
+  virtual LayoutManagerConstructor getLayoutManager(); // O(1)
+    // returns null
 }
 class TemplateElement : Element {
   constructor (Dictionary<String> attributes, ChildArguments... nodes); // O(M+N), M = number of attributes, N = number of nodes plus all their descendants
   constructor (ChildArguments... nodes); // shorthand
   constructor (Dictionary<String> attributes); // shorthand
   constructor (); // shorthand
   constructor attribute String tagName; // O(1) // "template"
   constructor attribute Boolean shadow; // O(1) // false
 
   readonly attribute DocumentFragment content; // O(1)
+  virtual LayoutManagerConstructor getLayoutManager(); // O(1)
+    // returns null
 }
 class ScriptElement : Element {
   constructor (Dictionary<String> attributes, ChildArguments... nodes); // O(M+N), M = number of attributes, N = number of nodes plus all their descendants
   constructor (ChildArguments... nodes); // shorthand
   constructor (Dictionary<String> attributes); // shorthand
   constructor (); // shorthand
   constructor attribute String tagName; // O(1) // "script"
   constructor attribute Boolean shadow; // O(1) // false
+
+  virtual LayoutManagerConstructor getLayoutManager(); // O(1)
+    // returns null
 }
 class StyleElement : Element {
   constructor (Dictionary<String> attributes, ChildArguments... nodes); // O(M+N), M = number of attributes, N = number of nodes plus all their descendants
   constructor (ChildArguments... nodes); // shorthand
   constructor (Dictionary<String> attributes); // shorthand
   constructor (); // shorthand
   constructor attribute String tagName; // O(1) // "style"
   constructor attribute Boolean shadow; // O(1) // false
 
   Array<Rule> getRules(); // O(N) in rules
+  virtual LayoutManagerConstructor getLayoutManager(); // O(1)
+    // returns null
 }
 class ContentElement : Element {
   constructor (Dictionary<String> attributes, ChildArguments... nodes); // O(M+N), M = number of attributes, N = number of nodes plus all their descendants
   constructor (ChildArguments... nodes); // shorthand
   constructor (Dictionary<String> attributes); // shorthand
   constructor (); // shorthand
   constructor attribute String tagName; // O(1) // "content"
   constructor attribute Boolean shadow; // O(1) // false
 
   Array<Node> getDistributedNodes(); // O(N) in distributed nodes
+  virtual LayoutManagerConstructor getLayoutManager(); // O(1)
+    // returns null
 }
 class ImgElement : Element {
   constructor (Dictionary<String> attributes, ChildArguments... nodes); // O(M+N), M = number of attributes, N = number of nodes plus all their descendants
   constructor (ChildArguments... nodes); // shorthand
   constructor (Dictionary<String> attributes); // shorthand
   constructor (); // shorthand
   constructor attribute String tagName; // O(1) // "img"
   constructor attribute Boolean shadow; // O(1) // false
+
+  virtual LayoutManagerConstructor getLayoutManager(); // O(1)
+    // returns ImgElementLayoutManager
 }
 class DivElement : Element {
   constructor (Dictionary<String> attributes, ChildArguments... nodes); // O(M+N), M = number of attributes, N = number of nodes plus all their descendants
   constructor (ChildArguments... nodes); // shorthand
   constructor (Dictionary<String> attributes); // shorthand
   constructor (); // shorthand
   constructor attribute String tagName; // O(1) // "div"
   constructor attribute Boolean shadow; // O(1) // false
 }
 class SpanElement : Element {
   constructor (Dictionary<String> attributes, ChildArguments... nodes); // O(M+N), M = number of attributes, N = number of nodes plus all their descendants
   constructor (ChildArguments... nodes); // shorthand
   constructor (Dictionary<String> attributes); // shorthand
   constructor (); // shorthand
   constructor attribute String tagName; // O(1) // "span"
   constructor attribute Boolean shadow; // O(1) // false
 }
 class IframeElement : Element {
   constructor (Dictionary<String> attributes, ChildArguments... nodes); // O(M+N), M = number of attributes, N = number of nodes plus all their descendants
   constructor (ChildArguments... nodes); // shorthand
   constructor (Dictionary<String> attributes); // shorthand
   constructor (); // shorthand
   constructor attribute String tagName; // O(1) // "iframe"
   constructor attribute Boolean shadow; // O(1) // false
+
+  virtual LayoutManagerConstructor getLayoutManager(); // O(1)
+    // returns IframeElementLayoutManager
 }
 class TElement : Element {
   constructor (Dictionary<String> attributes, ChildArguments... nodes); // O(M+N), M = number of attributes, N = number of nodes plus all their descendants
   constructor (ChildArguments... nodes); // shorthand
   constructor (Dictionary<String> attributes); // shorthand
   constructor (); // shorthand
   constructor attribute String tagName; // O(1) // "t"
   constructor attribute Boolean shadow; // O(1) // false
 }
 class AElement : Element {
   constructor (Dictionary<String> attributes, ChildArguments... nodes); // O(M+N), M = number of attributes, N = number of nodes plus all their descendants
   constructor (ChildArguments... nodes); // shorthand
   constructor (Dictionary<String> attributes); // shorthand
   constructor (); // shorthand
   constructor attribute String tagName; // O(1) // "a"
   constructor attribute Boolean shadow; // O(1) // false
 }
 class TitleElement : Element {
   constructor (Dictionary<String> attributes, ChildArguments... nodes); // O(M+N), M = number of attributes, N = number of nodes plus all their descendants
   constructor (ChildArguments... nodes); // shorthand
   constructor (Dictionary<String> attributes); // shorthand
   constructor (); // shorthand
   constructor attribute String tagName; // O(1) // "title"
   constructor attribute Boolean shadow; // O(1) // false
+
+  virtual LayoutManagerConstructor getLayoutManager(); // O(1)
+    // returns null
 }
 class ErrorElement : Element {
   constructor (Dictionary<String> attributes, ChildArguments... nodes); // O(M+N), M = number of attributes, N = number of nodes plus all their descendants
   constructor (ChildArguments... nodes); // shorthand
   constructor (Dictionary<String> attributes); // shorthand
   constructor (); // shorthand
   constructor attribute String tagName; // O(1) // "error"
   constructor attribute Boolean shadow; // O(1) // false
+
+  virtual LayoutManagerConstructor getLayoutManager(); // O(1)
+    // returns ErrorElementLayoutManager
 }
 
 callback InternalElementConstructor void (Module module);
 dictionary ElementRegistration {
   String tagName;
   Boolean shadow = false;
   InternalElementConstructor? constructor = null;
 }
 
 interface ElementConstructor {
@@ skipping 11 matching lines @@
 
   Boolean matches(Element element); // O(F())
   Element? find(Element root); // O(N*F())+O(M) where N is the number of descendants and M the average depth of the tree
   Element? find(DocumentFragment root); // O(N*F())+O(M) where N is the number of descendants and M the average depth of the tree
   Element? find(TreeScope root); // O(N*F()) where N is the number of descendants
   Array<Element> findAll(Element root); // O(N*F())+O(N*M) where N is the number of descendants and M the average depth of the tree
   Array<Element> findAll(DocumentFragment root); // O(N*F())+O(N*M) where N is the number of descendants and M the average depth of the tree
   Array<Element> findAll(TreeScope root); // O(N*F()) where N is the number of descendants
 }
 ```