Show graph of % CPU usage in Performance page

In the performance page, it would be nice if we could have a top chart (similar to timeline and memory) where we show an overview of the recorded activity. The overview for the performance page would be a graph of % CPU usage.

@bkonyi is this data available from the VM? Perhaps we could query percent CPU usage every ~100ms or so and graph it that way, or - even better - maybe we could hook up a stream and listen for percent usage events from the VM.

Start at the Performance page and determine whether the VM exposes percent CPU usage as queryable data or as a stream of usage events. Define the overview chart around the available data, using the existing timeline and memory charts as the behavioral reference. Done means the Performance page displays a recorded % CPU usage graph.

Scritto dal modello di indicizzazione a partire dal testo della issue.