[tracing] Implement process metrics data source

Bug: 374302723
Change-Id: I53fa505596be4a1bd24629d4bb46fcbbf1e54a6b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5966274
Reviewed-by: Francois Pierre Doray <fdoray@chromium.org>
Commit-Queue: Etienne Pierre-Doray <etiennep@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1375169}


CrOS-Libchrome-Original-Commit: 249abfc4379f62e046405bf9c3530074657fc869

Author: etiennep-chromium

base/trace_event/builtin_categories.h

@@ -264,6 +264,7 @@
   X(TRACE_DISABLED_BY_DEFAULT("network"))                                \
   X(TRACE_DISABLED_BY_DEFAULT("paint-worklet"))                          \
   X(TRACE_DISABLED_BY_DEFAULT("power"))                                  \
+  X(TRACE_DISABLED_BY_DEFAULT("process_metrics"))                        \
   X(TRACE_DISABLED_BY_DEFAULT("renderer.scheduler"))                     \
   X(TRACE_DISABLED_BY_DEFAULT("renderer.scheduler.debug"))               \
   X(TRACE_DISABLED_BY_DEFAULT("sequence_manager"))                       \