Refactor theme plugin loading.

In the old implementation, the QPlatformIntegration was asked
for the theme first, so there was no way of overriding that
by a custom plugin. Also, there was a memory leak in case
the platform theme was actually created by a plugin.

QGuiApplication now asks the QPlatformIntegration for a list
of potential theme names first, tries to load them using
the plugin loader and finally invokes a factory method of
QPlatformIntegration in case that fails. The theme is now
owned by QGuiApplication.

In the XCB plugin, the environment variable DESKTOP_SESSION
is queried and appended to the list of themes, making it possible
to load plugins for other session types.

Change-Id: I1a4b4e061815bca16c65b23e591bb7563a3e44e2
Reviewed-by: Samuel Rødal <samuel.rodal@nokia.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/src/plugins/platforms/windows/qwindowsintegration.h b/src/plugins/platforms/windows/qwindowsintegration.h
index 6dd65a02e4..20fd790bfe 100644
--- a/src/plugins/platforms/windows/qwindowsintegration.h
+++ b/src/plugins/platforms/windows/qwindowsintegration.h
@@ -69,7 +69,8 @@ public:
     virtual QPlatformAccessibility *accessibility() const;
     virtual QPlatformNativeInterface *nativeInterface() const;
     virtual QPlatformFontDatabase *fontDatabase() const;
-    virtual QPlatformTheme *platformTheme() const;
+    virtual QStringList themeNames() const;
+    virtual QPlatformTheme *createPlatformTheme(const QString &name) const;
     QPlatformServices *services() const;
     virtual QVariant styleHint(StyleHint hint) const;