Bug 1365309 - Part 4: Disable the BackgroundHangMonitor in GMP processes, r=froydnj

This involved a change to BackgroundHangMonitor, as it initialized sDisabled
incorrectly to false, instead of true, We need sDisabled initialized to true, as
we cannot assume that it is enabled until BackgroundHangMonitor::Startup() is
called.

MozReview-Commit-ID: 94slLTkNk3C

dom/media/gmp/GMPProcessChild.cpp

@@ -44,8 +44,6 @@ GMPProcessChild::Init(int aArgc, char* aArgv[])
 #error Not implemented
 #endif
 
-  BackgroundHangMonitor::Startup();
-
   return mPlugin.Init(pluginFilename,
                       ParentPid(),
                       IOThreadChild::message_loop(),
@@ -55,7 +53,6 @@ GMPProcessChild::Init(int aArgc, char* aArgv[])
 void
 GMPProcessChild::CleanUp()
 {
-  BackgroundHangMonitor::Shutdown();
 }
 
 } // namespace gmp

xpcom/threads/BackgroundHangMonitor.cpp

@@ -240,7 +240,7 @@ public:
 
 
 StaticRefPtr<BackgroundHangManager> BackgroundHangManager::sInstance;
-bool BackgroundHangManager::sDisabled = false;
+bool BackgroundHangManager::sDisabled = true;
 
 MOZ_THREAD_LOCAL(BackgroundHangThread*) BackgroundHangThread::sTlsKey;
 bool BackgroundHangThread::sTlsKeyInitialized;
@@ -720,6 +720,10 @@ BackgroundHangMonitor::Startup()
 #ifdef MOZ_ENABLE_BACKGROUND_HANG_MONITOR
   MOZ_ASSERT(!BackgroundHangManager::sInstance, "Already initialized");
 
+  // Enable the BackgroundHangManager by setting sDisabled to false in Startup.
+  MOZ_ASSERT(BackgroundHangManager::sDisabled);
+  BackgroundHangManager::sDisabled = false;
+
   if (!strcmp(NS_STRINGIFY(MOZ_UPDATE_CHANNEL), "beta")) {
     if (XRE_IsParentProcess()) { // cached ClientID hasn't been read yet
       BackgroundHangThread::Startup();