Bug 1552401 - Add and use a new decommit phase to attribute decommit work r=jonco

Differential Revision: https://phabricator.services.mozilla.com/D32090

--HG--
extra : moz-landing-system : lando

Author: PaulBone

js/src/gc/GC.cpp

@@ -3465,6 +3465,7 @@ void GCRuntime::decommitAllWithoutUnlocking(const AutoLockGC& lock) {
 }
 
 void GCRuntime::startDecommit() {
+  gcstats::AutoPhase ap(stats(), gcstats::PhaseKind::DECOMMIT);
   MOZ_ASSERT(CurrentThreadCanAccessRuntime(rt));
   MOZ_ASSERT(!decommitTask.isRunning());
 

js/src/gc/GenerateStatsPhases.py

@@ -159,6 +159,7 @@ def __init__(self, name, descr, bucket, children=[]):
             JoinParallelTasksPhaseKind
         ]),
     ]),
+    PhaseKind("DECOMMIT", "Decommit", 72),
     PhaseKind("GC_END", "End Callback", 44),
     PhaseKind("MINOR_GC", "All Minor GCs", 45, [
         MarkRootsPhaseKind,