[ETW Export] Add polling for ETW keyword.
This adds a background low-priority thread for each process that monitors the keyword and adjusts the categories accordingly. This allows users to start profiling (using UIForETW or Xpef directly) and specify which categories to enable, without having to restart Chrome.
Notes:
- TraceEventETWExport is a friend of TraceLog (see comment in code).
- ETW exporting still needs to be enabled using the command line or in about:flags.
BUG=491909
Review URL: https://codereview.chromium.org/1279353002
Cr-Commit-Position: refs/heads/master@{#343393}
CrOS-Libchrome-Original-Commit: 3bd527974c0cea7b1e0e9965fa9e13823861ebb6
2 files changed