QmlProfiler: skip computing fps when not going to display them

Change-Id: I808f8a3b1cb6243f7df40bb1747d9ca92fb80380
Reviewed-on: http://codereview.qt.nokia.com/455
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Kai Koehne <kai.koehne@nokia.com>

src/plugins/qmlprofiler/qml/MainView.js

@@ -59,6 +59,7 @@ function reset()
 
 function calcFps()
 {
+    if (drawFpsGraph) {
         if (values.length)
             frameFps = new Array(values.length - 1);
         for (var i = 0; i < values.length - 1; ++i) {
@@ -66,6 +67,7 @@ function calcFps()
             frameFps[i] = 1000 / frameTime;
         }
     }
+}
 
 //draw background of the graph
 function drawGraph(canvas, ctxt, region)