Chrome extension: update packaged PDF.js code to v1.0.907

Since now we support PDF.js v1.0.907, there is no reason to ship anything less than the latest and greatest in our Chrome extension.

There is only one caveat, and that's the sole reason the WIP is in the name: there is a CSS (?) problem which makes our highlights invisible with PDF.js v1.0.907.

The classes are there, the CSS rules are there - but they just don't show.

This problem is not limited to Chrome: FF35 beta, which ships the same PDF.js version, has the same problem.

I'll open a separate ticket for that; we should probably postpone shipping this until that problem is solved.