void methods are not testable. so we need to make then to return error code

[Suresh-Babu-K]

void methods are not testable. so we need to make then to return error code

this look challenging as we did not designed the whole code as testable one.

void CpuCostModel::PrepareStats(FlowGraphNode* accumulator) .. if this would have returned an error code we know that action is completed properly .