ComboBox: Fix style content size calculation

Expression taken from QComboBox. Also, cleaner way of setting the
popup item font size where needed.

Change-Id: Ic6997e8d887dafc519a3827c2a40cb8f91503ebc
Reviewed-by: Jens Bache-Wiig <jens.bache-wiig@digia.com>

src/controls/ComboBox.qml

@@ -104,7 +104,11 @@ Control {
         onPressedChanged: if (pressed) popup.show()
     }
 
-    StyleItem { id: styleItem }
+    StyleItem {
+        id: styleItem
+        elementType: "comboboxitem"
+        visible: false
+    }
 
     Component.onCompleted: {
         if (currentIndex === -1)
@@ -112,7 +116,6 @@ Control {
         if (styleItem.style == "mac") {
             popup.x -= 10
             popup.y += 4
-            popup.__font.pointSize = 13
         }
 
         popup.ready = true
@@ -136,6 +139,7 @@ Control {
         property int y: isPopup ? (comboBox.__panel.height - comboBox.__panel.implicitHeight) / 2.0 : comboBox.__panel.height
         __minimumWidth: comboBox.width
         __visualItem: comboBox
+        __font: styleItem.font
 
         property ExclusiveGroup eg: ExclusiveGroup { id: eg }
 

src/styles/Desktop/ComboBoxStyle.qml

@@ -54,7 +54,8 @@ Style {
         enabled: control.enabled
         text: control.currentText
         hasFocus: control.activeFocus
-        contentHeight: 18
+        // contentHeight as in QComboBox
+        contentHeight: Math.max(Math.ceil(textHeight("")), 14) + 2
         contentWidth: textWidth(text)
     }