Bug 1993818 - Don't add battery observer after xpcom-will-shutdown. r=bradwerth

In bug 1981068 we made GPUProcessManager remove its battery observer
in xpcom-will-shutdown rather than xpcom-shutdown, to ensure there are
no outstanding observers when MacPowerInformationService shuts down in
response to xpcom-shutdown. However, if the GPU process launch
completes after xpcom-will-shutdown but before xpcom-shutdown, then we
will create a new battery observer, causing the assertion that there
are no outstanding observers during xpcom-shutdown to fail.

This patch avoids this by checking the shutdown phase prior to
creating the observer. Temporarily running without the observer is
harmless, and the GPU process will be shutdown imminently anyway.

Differential Revision: https://phabricator.services.mozilla.com/D272843

UltraBlame original commit: 4c3e758d1aecdef721408ab77bffb5c04e4314a8

Author: marco-c

gfx/ipc/GPUProcessManager.cpp

@@ -4079,13 +4079,29 @@ MOZ_DIAGNOSTIC_ASSERT
 mBatteryObserver
 )
 ;
+if
+(
+!
+AppShutdown
+:
+:
+IsInOrBeyond
+(
+ShutdownPhase
+:
+:
+XPCOMWillShutdown
+)
+)
+{
 mBatteryObserver
 =
 new
 BatteryObserver
 (
 )
 ;
+}
 /
 /
 Flush