I read in http://qt-project.org/wiki/QtWebEngine in the Windows, "MSVC" is necessary to compile to work with the "Chromium".
Windows (MSVC 2013 packages).
And QtWebkit will no updates (http://qt-project.org/wiki/New-Features-in-Qt-5.4):
The Qt WebKit module is considered done. It will in future be replaced by Qt WebEngine.
Should be discouraged from developing using "MingW"?
I suggest two ways:
Continue the support QtWebKit in parallel to QtWebEngine.
Discontinue MingW in QT.
Note: Unless you say that in the future it is likely that the "Chromium" has plans to support "MingW" (or MingW evolve and support the necessary dependancy) then disregard this suggestion.