Tests the load event.

Page reloaded.
Model records:
MarkDOMContent Properties:
{
    counters : <object>
    data : {
        isMainFrame : true
    }
    frameId : <string>
    startTime : <number>
    type : "MarkDOMContent"
    usedHeapSize : <number>
}
MarkLoad Properties:
{
    counters : <object>
    data : {
        isMainFrame : true
    }
    frameId : <string>
    startTime : <number>
    type : "MarkLoad"
    usedHeapSize : <number>
}
Timestamp records:
MarkDOMContent Properties:
{
    counters : <object>
    data : {
        isMainFrame : true
    }
    frameId : <string>
    startTime : <number>
    type : "MarkDOMContent"
    usedHeapSize : <number>
}
MarkLoad Properties:
{
    counters : <object>
    data : {
        isMainFrame : true
    }
    frameId : <string>
    startTime : <number>
    type : "MarkLoad"
    usedHeapSize : <number>
}