The interface of all of the "image" streams look kind of weird, and I'm actually a bit surprised that there hasn't been any errors because of it.
For example: None of them actually implement `readBlock` methods, and it seems more luck that anything else that we're not calling `getBytes()` (without providing a length) for those streams, since that would trigger a code-path in `getBytes` that assumes `readBlock` to exist.
To address this long-standing issue, the `ensureBuffer` methods are thus renamed to `readBlock`. Furthermore, the new `ensureBuffer` methods are now no-ops.
Finally, this patch also replaces `var` with `let` in a number of places.
By making use of modern CSS features, in this case [CSS variables](https://developer.mozilla.org/en-US/docs/Web/CSS/Using_CSS_variables), implementing sidebar resizing is actually quite simple. Not only will the amount of added code be fairly small, but it should also be easy to maintain since there's no need for complicated JavaScript hacks in order to update the CSS. Another benefit is that the JavaScript code doesn't need to make detailed assumptions about the exact structure of the HTML/CSS code.
Obviously this will not work in older browsers, such as IE, that lack support for CSS variables. In those cases sidebar resizing is simply disabled (via feature detection), and the resizing DOM element hidden, and the behaviour is thus *identical* to the current (fixed-width) sidebar.
However, considering the simplicity of the implementation, I really don't see why limiting this feature to "modern" browsers is a problem.
Finally, note that a few edge-cases meant that the patch is a bit larger than what the basic functionality would dictate. Among those is first of all proper RTL support, and secondly (automatic) resizing of the sidebar when the width of the *entire* viewer changes. Another, pre-existing, issue fixed here is the incomplete interface of `NullL10n`.
*Please note:* This patch has been successfully tested in both LTR and RTL viewer locales, in recent versions of Firefox and Chrome.
Fixes 2072.
https://eslint.org/docs/rules/no-var
Please note that two files were excluded:
1. `web/debugger.js`, since there's code in other files that currently depend on the global availability of code in `web/debugger.js`. Furthermore, since that file isn't used in production, doing a ES6 conversion probably isn't a priority.
2. `web/grab_to_pan.js`, since that file could be considered to be "external" code. We have made smaller changes to that file over the years, however doing a full ES6 `class` conversion might be a step too far!?
In the PDF file, the `ToUnicode` data first maps the hyphen correctly, and then *overwrites* it to point to the softhyphen instead. That one cannot be rendered in browsers, and an empty space thus appear instead.
Fixes 9084.
