client api: Introduce a bare-bones TrackEvent library

This patch adds a basic TrackEvent library to serve as a higher level
entrypoint into Perfetto for apps that wish to record various types of
events on a timeline. For now, the library only supports explicit
Begin/End slice events with static categories and names. Note that
enabling trace points based on their categories isn't supported yet.

Bug: 132678367
Change-Id: If72eb0c0cba565303b0a778933931609043c5004
diff --git a/Android.bp b/Android.bp
index 7ec6c76..372b9f2 100644
--- a/Android.bp
+++ b/Android.bp
@@ -515,6 +515,7 @@
     "src/tracing/platform_posix.cc",
     "src/tracing/trace_writer_base.cc",
     "src/tracing/tracing.cc",
+    "src/tracing/track_event.cc",
     "src/tracing/virtual_destructors.cc",
   ],
   shared_libs: [
@@ -892,6 +893,7 @@
     "src/tracing/platform_posix.cc",
     "src/tracing/trace_writer_base.cc",
     "src/tracing/tracing.cc",
+    "src/tracing/track_event.cc",
     "src/tracing/virtual_destructors.cc",
     "test/end_to_end_integrationtest.cc",
     "test/fake_producer.cc",