Set transformOrigin for text layer in css.

transformOrigin is set to 0% 0% in all cases. This adds extra memory
impact into the dom tree. It also involves the CustomStyles workaround
to determine the correct css rule for the browser.
By setting all vendor and standard variants in css, the rule is applied
without the dom memory overhead and without the minor computation
overhead to set the value.
no need to set textlayer properties which are overwritten in individual styles.
Merge pull request #5209 from CodingFabian/text-layer-transform-origin

Set transformOrigin for text layer in css.
Avoid creating intermediate strings in sanitizeMetrics

This patch avoids creating many intermediate strings, when adding dummy width/lsb entries for glyphs where those are missing.
For the relevant PDF files in our test suite, the average number of intermediate strings are well over 1000.
Merge pull request #5219 from Snuffleupagus/sanitizeMetrics-avoid-intermediate-strings

Avoid creating intermediate strings in sanitizeMetrics
Chrome extension: Isolate pageAction logic

Remove pageAction logic from extension router, and put it in a
separate file. The pageAction URL parsing logic has been simplified,
and all pageAction-related files have been moved to a separate directory.
Merge pull request #5232 from Rob--W/crx-isolate-pageAction-logic

Chrome extension: Isolate pageAction logic
In src/display/api.js, add documentation for the |progressCallback| parameter in |PDFJS.getDocument|
Merge pull request #5240 from Snuffleupagus/api-progressCallback-doc

In src/display/api.js, add documentation for the |progressCallback| parameter in |PDFJS.getDocument|
Added an help button in the menu that displays a guided tour of the UI