Flow related to Document object and LocalFrame

[jungle panda]

I tried loading a simple hello world webpage with few logs in blink code.

I have following doubts -

1) The document constrcuctor is called twice. For the first time document has only 3 tags html,head,body and when the constructor is called the second time then it has all the tags metioned on the webpage, why so?

2) If we insert a Iframe inside the webpage then it creates a LocalFrame for main frame and iframe. so is there any frame tree that gives the information about which iframe is mapped to which iframe tag inside main frame ? where can I print the frame tree ?

3) I am not able to find in which file document object is created. I just know that its constructor is called twice for a simple webpage without iframes.

Please let me know if anyone can provide any help in this regard.

Thanks.