Adjust gn and ifdefs to make Perfetto available

This change adjusts some ifdefs and also updates two .gn files to enable
Perfetto on Windows in Chromium.

This change makes no difference unless the command-line option
--enable-features=TracingPerfettoBackend is specified, which can be
tested with:

  chrome.exe --trace-startup= --trace-startup-file=test.json ^
    --trace-startup-duration=7 --enable-features=TracingPerfettoBackend

This was originally landed in crrev.com/c/1064371

Bug: 844421, 844379
Change-Id: I2f4049b8623003d6c64ae942f0c334b1fc83875d
Reviewed-on: https://chromium-review.googlesource.com/1090756
Commit-Queue: oysteine <oysteine@chromium.org>
Reviewed-by: oysteine <oysteine@chromium.org>
Cr-Commit-Position: refs/heads/master@{#576590}
4 files changed