Don't make the output pane get taller when switching tabs.

A code review change broke the logic. Revise to avoid this bug.
Load the saved height once at startup and save it at app close.
Track changes to the height as they happen.
This ensures the output pane does not get taller if you shrink
it and then switch tabs.

Task-number: QTCREATORBUG-8877
Change-Id: If0d0d0d45f2944477003eb407e64567441bad414
Reviewed-by: Eike Ziller <eike.ziller@digia.com>

src/plugins/coreplugin/outputpanemanager.cpp

@@ -121,7 +121,8 @@ OutputPaneManager::OutputPaneManager(QWidget *parent) :
     m_opToolBarWidgets(new QStackedWidget),
     m_minimizeIcon(QLatin1String(":/core/images/arrowdown.png")),
     m_maximizeIcon(QLatin1String(":/core/images/arrowup.png")),
-    m_maximised(false)
+    m_maximised(false),
+    m_outputPaneHeight(0)
 {
     setWindowTitle(tr("Output"));
 
@@ -376,6 +377,8 @@ void OutputPaneManager::readSettings()
         if (visibility.contains(m_ids.at(i).toString()))
             m_buttons.at(i)->setVisible(visibility.value(m_ids.at(i).toString()));
     }
+
+    m_outputPaneHeight = settings->value(QLatin1String("OutputPanePlaceHolder/Height"), 0).toInt();
 }
 
 void OutputPaneManager::slotNext()
@@ -473,8 +476,6 @@ void OutputPaneManager::showPage(int idx, int flags)
     }
 
     if (ph) {
-        QSettings *settings = ICore::settings();
-        int height = settings->value(QLatin1String("OutputPanePlaceHolder/Height"), 0).toInt();
         // make the page visible
         ph->setVisible(true);
         ensurePageVisible(idx);
@@ -485,7 +486,7 @@ void OutputPaneManager::showPage(int idx, int flags)
             ICore::raiseWindow(m_outputWidgetPane);
         }
 
-        ph->setDefaultHeight(height);
+        ph->setDefaultHeight(m_outputPaneHeight);
         if (flags & IOutputPane::EnsureSizeHint)
             ph->ensureSizeHintAsMinimum();
     } else {
@@ -508,6 +509,13 @@ void OutputPaneManager::focusInEvent(QFocusEvent *e)
         w->setFocus(e->reason());
 }
 
+void OutputPaneManager::resizeEvent(QResizeEvent *e)
+{
+    if (e->size().height() == 0)
+        return;
+    m_outputPaneHeight = e->size().height();
+}
+
 void OutputPaneManager::setCurrentIndex(int idx)
 {
     static int lastIndex = -1;
@@ -572,12 +580,7 @@ void OutputPaneManager::saveSettings() const
         settings->setValue(QLatin1String(outputPaneVisibleKeyC), m_buttons.at(i)->isVisible());
     }
     settings->endArray();
-    OutputPanePlaceHolder *ph = OutputPanePlaceHolder::getCurrent();
+    settings->setValue(QLatin1String("OutputPanePlaceHolder/Height"), m_outputPaneHeight);
-    if (ph) {
-        int height = ph->height();
-        if (height)
-            settings->setValue(QLatin1String("OutputPanePlaceHolder/Height"), height);
-    }
 }
 
 void OutputPaneManager::clearPage()

src/plugins/coreplugin/outputpanemanager.h

@@ -75,6 +75,7 @@ public slots:
 
 protected:
     void focusInEvent(QFocusEvent *e);
+    void resizeEvent(QResizeEvent *e);
 
 private slots:
     void showPage(int flags);
@@ -132,6 +133,7 @@ private:
     QPixmap m_minimizeIcon;
     QPixmap m_maximizeIcon;
     bool m_maximised;
+    int m_outputPaneHeight;
 };
 
 class OutputPaneToggleButton : public QToolButton