Core: Fix build.

Change-Id: Id11aadb251a91bc579979dab971ea45960aabb86
Reviewed-by: hjk <hjk121@nokiamail.com>

src/plugins/coreplugin/id.cpp

@@ -32,6 +32,7 @@
 #include <utils/qtcassert.h>
 
 #include <QByteArray>
+#include <QDataStream>
 #include <QHash>
 #include <QVariant>
 

src/plugins/coreplugin/id.h

@@ -35,7 +35,10 @@
 #include <QMetaType>
 #include <QString>
 
-QT_FORWARD_DECLARE_CLASS(QVariant)
+QT_BEGIN_NAMESPACE
+class QDataStream;
+class QVariant;
+QT_END_NAMESPACE
 
 namespace Core {