Html 5 stroke() is much slower in Qt 5 than in Qt 4.8.x

Drawing a lot of lines (for example a triangular wave with short wave length) with stroke() on html 5 canvas takes really long time in Qt5 compared to Qt4.8.x. The problem can be reproduced with the attached html/javascript file (testijs.html) in Qt's Fancy Browser example. Just open the file and wait until it is rendered. In Qt 4.8.x it takes a couple of seconds and in Qt5 it takes around 30 seconds on Windows 7.

I also ran the javascript through the http://jsperf.com/ performance test and it gave the following results (on Windows 7):
FancyBrowser Qt5.1.0: 1.68 operations/sec
FancyBrowser Qt4.8.5: 8.08 operations/sec
Chrome(for reference): 12.60 operations/sec

This has been tested in Qt 5.0, 5.1.1, 5.2 with or without OpenGL support, in release and in debug builds, and on Windows, Linux and Mac.