Fix escape logic for closing find tool bar in mode with editor view

E.g. open context help, press ctrl+f to search in help, press escape
(focus moves to help viewer), press escape: find tool bar should be
hidden, instead it was moving focus to the editor.

Change-Id: Ia5d8563458582e2871afd9e3107e49e71d03b3f5
Reviewed-by: Daniel Teske <daniel.teske@digia.com>

src/plugins/coreplugin/findplaceholder.cpp

@@ -63,6 +63,20 @@ QWidget *FindToolBarPlaceHolder::owner() const
     return m_owner;
 }
 
+/*!
+ * Returns if \a widget is a subwidget of the place holder's owner
+ */
+bool FindToolBarPlaceHolder::isUsedByWidget(QWidget *widget)
+{
+    QWidget *current = widget;
+    while (current) {
+        if (current == m_owner)
+            return true;
+        current = current->parentWidget();
+    }
+    return false;
+}
+
 void FindToolBarPlaceHolder::setWidget(QWidget *widget)
 {
     if (m_subWidget) {