Disable Range Support for Chrome 39+40 (#5512)

[CodingFabian]

Disabling Range Support for Chrome 39 and above, due to regression in
Chromium. Will be enabled once a fix version is confirmed.

• https://code.google.com/p/chromium/issues/detail?id=444659
• https://code.google.com/p/chromium/issues/detail?id=442318

[Rob--W]

As I said at #5512 (comment), disabling range requests has a huge impact on perceived performance, so disabling range requests should be the last course of action.

Fortunately, there is a way to resolve the issue without disabling range requests: #5603. Hence I suggest to close this PR in favor of #5603.

[yurydelendik]

Let's see when it will be fixes, and when the fixes reaches the release version of Chrome we replace #5603 with this fix.

[CodingFabian]

just to keep on the top of this.
in https://code.google.com/p/chromium/issues/detail?id=442318 it is confirmed that this is broken in chrome 39 and 40. Fix will be going to 41. So we might consider using my patch and disable range requests for those two versions.

[Rob--W]

web/compatibility.js is not loaded in the Chrome extension, so please wait at least two release cycles before merging (and reverting https://github.com/mozilla/pdf.js/pull/5603/files).

I've sent a mail last week to the CWS, and requested information about the browser version usage stats in order to determine when it is safe to drop support for a certain Chrome version, but I have yet to hear back from them. Until that happens, I want to be conservative in dropping features that may affect users of the Chrome extension.

[timvandermeij]

The upstream bug appears to be fixed and it has been a couple of months, so is there anything left to be done here?

[Rob--W]

The Chrome bug only exists in 39 and 40, so this PR should be amended, e.g. by changing the isChromeWithRangeBug declaration to

// Range requests are broken in Chrome 39 and 40, https://crbug.com/442318
var isChromeWithRangeBug = /Chrome\/(39|40)\./.test(navigator.userAgent);

#5603 can be reverted together with this change.

Or we can ignore the backcompat code, since most Chrome users are supposedly using the latest stable version due to auto-update (in contrast to old Android, which doesn't get auto-updated). Then I will revert #5603 as a part of a patch that removes backcompat code from the Chrome extension.

[CodingFabian]

I have amended this pr. I would propose to merge it and revert #5603

[timvandermeij]

/botio-linux preview

[pdfjsbot]

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• B2G Viewer: http://107.21.233.14:8877/15bbf57b077e3fe/extensions/b2g/content/web/viewer.html
• Extension: http://107.21.233.14:8877/15bbf57b077e3fe/extensions/firefox/pdf.js.xpi

[timvandermeij]

Fixes #5512.

[timvandermeij]

Looks good, thank you! I'll follow this up with reverting #5603.