Restore support for -title command line argument on X11, add -qwindowtitle.

-title disappeared between Qt4 and Qt5, due to all the refactorings around QPA.
Making the caption of the mainwindow configurable allows custom setups
for specific users or use cases.

[ChangeLog][QtGui][QGuiApplication] Restore support for -title command line
argument on X11, add -qwindowtitle on all platforms.

Change-Id: I73e6bf21248f3419178eba583b257172a175e74e
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Albert Astals Cid <albert.astals@canonical.com>
Reviewed-by: Paul Olav Tvete <paul.tvete@digia.com>
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@digia.com>

src/gui/kernel/qguiapplication.cpp

@@ -471,6 +471,8 @@ static QWindowGeometrySpecification windowGeometrySpecification;
             and will make the application wait until a debugger connects to it.
         \li  -session \e session, restores the application from an earlier
             \l{Session Management}{session}.
+        \li  -qwindowgeometry, sets the geometry of the first window
+        \li  -qwindowtitle, sets the title of the first window
     \endlist
 
     \sa arguments()
@@ -1033,6 +1035,9 @@ void QGuiApplicationPrivate::createPlatformIntegration()
         } else if (arg == "-qwindowgeometry" || (platformName == "xcb" && arg == "-geometry")) {
             if (++i < argc)
                 windowGeometrySpecification = QWindowGeometrySpecification::fromArgument(argv[i]);
+        } else if (arg == "-qwindowtitle" || (platformName == "xcb" && arg == "-title")) {
+            if (++i < argc)
+                firstWindowTitle = QString::fromLocal8Bit(argv[i]);
         } else {
             argv[j++] = argv[i];
         }

src/gui/kernel/qguiapplication_p.h

@@ -231,6 +231,8 @@ public:
     static bool noGrab;
     QInputMethod *inputMethod;
 
+    QString firstWindowTitle;
+
     static QList<QObject *> generic_plugin_list;
 #ifndef QT_NO_SHORTCUT
     QShortcutMap shortcutMap;

src/gui/kernel/qwindow.cpp

@@ -432,6 +432,14 @@ void QWindow::setVisible(bool visible)
         // remove posted quit events when showing a new window
         QCoreApplication::removePostedEvents(qApp, QEvent::Quit);
 
+        if (type() == Qt::Window) {
+            QString &firstWindowTitle = QGuiApplicationPrivate::instance()->firstWindowTitle;
+            if (!firstWindowTitle.isEmpty()) {
+                setTitle(firstWindowTitle);
+                firstWindowTitle = QString();
+            }
+        }
+
         QShowEvent showEvent;
         QGuiApplication::sendEvent(this, &showEvent);
     }

tests/auto/gui/kernel/qguiapplication/tst_qguiapplication.cpp

@@ -60,6 +60,7 @@ class tst_QGuiApplication: public tst_QCoreApplication
 
 private slots:
     void displayName();
+    void firstWindowTitle();
     void focusObject();
     void allWindows();
     void topLevelWindows();
@@ -83,6 +84,17 @@ void tst_QGuiApplication::displayName()
     QCOMPARE(QGuiApplication::applicationDisplayName(), QString::fromLatin1("The GUI Application"));
 }
 
+void tst_QGuiApplication::firstWindowTitle()
+{
+    int argc = 3;
+    char *argv[] = { const_cast<char*>("tst_qguiapplication"), const_cast<char*>("-qwindowtitle"), const_cast<char*>("User Title") };
+    QGuiApplication app(argc, argv);
+    QWindow window;
+    window.setTitle("Application Title");
+    window.show();
+    QCOMPARE(window.title(), QString("User Title"));
+}
+
 class DummyWindow : public QWindow
 {
 public: