Include top content margin in GpuDebugMarker (#3515)
Include top content margin in GpuDebugMarker (#3515)

It's included in GetHeight() but not in the position of the timers, as
it is in other tracks/subtracks. This margin was being included in the
bottom margin of that subtrack.

http://b/218516297
google/orbit,google/orbit,google/orbit,google/orbit