Qt 5.2's QWebView does not support plugin. Because not PluginPackageMac.cpp but PluginPackageNone.cpp is used.

The following description was added 　qtwebkit/Tools/qmake/mkspecs/features/unix/default_pre.prf of Qt 5.2.

# If Qt is configured with embedded or QPA we set a convenience config
# flag that can be used to test for either of these situations.
contains(QT_CONFIG, qpa)|contains(QT_CONFIG, embedded): CONFIG += embedded

QT_CONFIG contains qpa on Mac OS X, So QtWebkit's config contain embedded flag.

PluginPackageNone.cpp is used with embedded flag by qtwebkit/Tools/qmake/mkspecs/features/features.prf