Create more instances for object graph walk

To find `[NoInterfaceObject]` interfaces and properties that occur on instances instead of prototypes (eg. `CSSStyleDeclaration`), we must discover some instances. For now we do some sort of limited walk from `window`, but IIRC it's not a full recursive walk. Even if it was, there are still interesting instances we couldn't find without invoking some methods.

As foolip mentions in https://github.com/GoogleChrome/confluence/issues/163#issuecomment-331441582, I suggest we add a list of expressions as a heuristic to ensure we discover specific instances of value (eg. `document.body.style`). Then we can augment this list manually whenever we find something that's missing (while still aiming to discover most things automatically).