TraceTests: Add a screenshot frame member variable Instead of modifying a global when detecting KeyFrames are in use by a trace, update a new value tracked per trace. Also consolidate the option handling for gRunToKeyFrame since its needs align with gMaxStepsPerformed. Test: Batching traces that include one with a keyframe Bug: angleproject:8035 Bug: b/270426257 Change-Id: I2ed4215d9f310dddb317debf09921aa45c6822bf Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/4288616 Reviewed-by: Yuxin Hu <yuxinhu@google.com> Commit-Queue: Cody Northrop <cnorthrop@google.com>