Only acquire resources as required in gstreamer backend.

Make resources required for capture optional and disable just the
capture features if they are not available, so the camera viewfinder
can be displayed and images captured without blocking the music
playback and the other way around.

Change-Id: Ic9692195156d994ccd4a911ae41d2242a00d575b
Reviewed-by: John Brooks <john.brooks@dereferenced.net>
Reviewed-by: Yoann Lopes <yoann.lopes@digia.com>

src/plugins/gstreamer/camerabin/camerabinresourcepolicy.h

@@ -69,18 +69,27 @@ public:
 
     bool isResourcesGranted() const;
 
+    bool canCapture() const;
+
 Q_SIGNALS:
     void resourcesDenied();
     void resourcesGranted();
     void resourcesLost();
+    void canCaptureChanged();
 
 private Q_SLOTS:
+    void handleResourcesLost();
+    void handleResourcesGranted();
     void handleResourcesReleased();
+    void resourcesAvailable();
+    void updateCanCapture();
+
 
 private:
     ResourceSet m_resourceSet;
     ResourcePolicy::ResourceSet *m_resource;
     bool m_releasingResources;
+    bool m_canCapture;
 };
 
 QT_END_NAMESPACE