selectAll: Get rid of dependency of |editing.dom| for committing to Blink repository.
[testing] Make not to set focus when executing test cases for "selectAll" command test cases works as what Chrome does.
Note: focus element, aka document.activeElement, affects only "selectAll" on SELECT element.
selectAll: Get rid of using |EditingContext| for Blink committing.
Change |CommandFunction| to take |Document| rather than |editing.EditingContext| for supporting not undoable commands, e.g. "selectAll", "useCSS".
undo: Make "undo" and "redo" command as not undoable commands.
Rename |Editor.prototype.getDomSelection()| to |Editor.prototype.getSelectionFromDom()|, since this function returns |ImmutableSelection| rather than |Selection|.