Fix a couple of mislabled atrace markers and add explicit markers
for inside/outside renderpass flushes.

Bug: b/156403378
Change-Id: I4045846e54ff54bc8fc3dd6ef47339f6f5eb8e87
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2327828Reviewed-by: Courtney Goeltzenleuchter <courtneygo@google.com>
Reviewed-by: Tobin Ehlis <tobine@google.com>
Commit-Queue: Tobin Ehlis <tobine@google.com>