<object> / <embed> support in Chrome / Opera

This PR brings support for embedded PDFs of the following forms:

```
<object type="application/pdf" data="...">
<embed type="application/pdf" src="...">
<object data="....pdf"> <!-- note: no type specified -->
<embed src="....pdf"> <!-- note: no type specified -->
```

Fixes https://github.com/operasoftware/pdf.js/issues/19
Fixes #3736
Supersedes #4194

##### Tests
To check whether the feature works as intended, visit the following pages, and check whether the PDF viewer is rendered:

- http://plugindoc.mozdev.org/testpages/pdf.html
- http://acroeng.adobe.com/wp/?page_id=161 (all 9 examples)
- http://pdfpiw.uspto.gov/.piw?Docid=08000431&homeurl=http%3A%2F%2Fpatft.uspto.gov%2Fnetacgi%2Fnph-Parser%3FSect1%3DPTO2%2526Sect2%3DHITOFF%2526p%3D1%2526u%3D%25252Fnetahtml%25252FPTO%25252Fsearch-bool.html%2526r%3D1%2526f%3DG%2526l%3D50%2526co1%3DAND%2526d%3DPTXT%2526s1%3D3,257,285%2526OS%3D3,257,285%2526RS%3D3,257,285&PageNum=&Rtype=&SectionNum=&idkey=NONE&Input=View+first+page