The Chrome extension activates PDF.js by inserting the script tags
in a document whose URL and location origin is identical to the PDF
file.
Because of this, the path './images/' was resolved relatively to the
location of the PDF file instead of the extension.
To fix this, the IMAGE_DIR constant is moved outside the local scope,
to allow extensions/chrome/insertviewer.js to override the value.
Originally, the IMAGE_DIR variable was a global variable, but commit
f8f4b3f45d moved the global variable
to the local scope, causing the extension to malfunction.
Impact: low, the only consequence is that some rarely used images
were not visible.
Trivial test:
At the center of page 2, the annotation icon
(images/annotation-comment.svg) should be visible:
http://linorg.usp.br/CTAN/macros/latex/contrib/pdfcomment/doc/pdfcomment.pdf
