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

[Rob--W]

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 operasoftware#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

[Rob--W]

I will revisit this PR, and try to make it even more performant.

Without the patch, the second DOM benchmark at http://dromaeo.com/?dom-mod peeks around 700-900MB memory. With the patch, it triples to ~2.2 GB, and occasionally freezes for a second due to Garbage collection.

A quick test with a mutation observer and a no-op callback shows that the use of mutation observer is not necessarily the bottleneck.

[Rob--W]

@yurydelendik
Could you review this PR? I switched to a different method that does not have any negative impact on the performance of DOM.

[Rob--W]

@timvandermeij I want to prepare an update of the Chrome extension. Could you test this PR and merge it?

[timvandermeij]

Nice work, thanks!