chrome.runtime -> chrome.extension when needed

Some Ubuntu users are still stuck at Chromium 25.
Merge pull request #3807 from Rob--W/crx-chromium-25

chrome.runtime -> chrome.extension when needed (support Chromium 20-25)
Add missing jsdocs for PDFJS globals.
Inline setScale in parseScale
extract code to own method for faster JPX decoding
Merge pull request #3787 from Snuffleupagus/inline-setScale

Inline setScale in parseScale
Merge pull request #3796 from brendandahl/global-docs

Add missing jsdocs for PDFJS globals.
Minor nit fixes for api.js
Merge pull request #3810 from timvandermeij/nit-fixes

Minor nit fixes for api.js
Merge pull request #3554 from fkaelberer/FasterJPXdecoding

Speed up JPX decoding on Firefox