Add a tracing API and instrument key functions in order to profile aapt2 bottleneck. The API allows to generate systrace fragment files. Impact on performance is neglibible with each Trace requiring less than 1us and the final Flush operation at the end of a command requiring around 40us. Bug: None Test: None Change-Id: I51b564d3694e9384679f43b878b32295527dddf6