Need api to have option to pass down timestamps for cpu profiles

The problem is that apps already have timing callbacks which have recorded timings. But there is no way to pass these into the api. For a vulkan app, that can only do cpu profiling, there is no way to pass through the timestamps or gpu correlated timestamps to PIX. My understanding is that PIX hides the timestamps because it's trying to correlate it's own gpu and cpu timestamps. But that API should be exposed.

Callers can do QPC and then hand down the timestamp, although in my app, we convert QPC * (1/QPF) = double time in seconds. Also Vulkan apps can correlate gpu timestamps, and then hand those in QPC epoch.

The issue names no files, tests, or entry points. Start by locating the public CPU profiling API and its timestamp-handling documentation, then clarify the accepted units and epoch for QPC and GPU-correlated timestamps. Done means callers can pass recorded timestamps through the API and PIX can consume them for Vulkan CPU profiling.