Line height not always correctly updated after font change

[rkwright]

This issue is a Bug

Related issue(s) and/or pull request(s)

See ResizeSensor thread, #308

Expected Behaviour

Line height should be set correctly on the current page after a font change

Observed behaviour

Instead, Readium does not always set the line height for the current page to the right value. This is apparently because the computed height hasn't been completed when we go to re-layout the page. The font has been changed but the computedStyle isn't done yet.

Since it is a form of race condition the problem doesn't always occur. It is hard to reproduce in the Chrome JSApp, but relatively easily reproduced in the CloudReader on Safari on OSX.

Steps to reproduce

1. Open a page in some EPUB
2. Change the font so that the line-height changes
3. Examine the line-height. Note that it is not correct (not always but usually)
4. Move to the next (or previous page). Note that line-height is now correct.
5. Go back to the original page (on which the font was changed).
6. NOW the line-height is correct.

Test file(s)

Pretty much any. Accessible EPUB, for example.

Product

Any Readium-1 based app which uses the font layout machinery in shared-js

Additional information

None

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@danielweck
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