Revert of Do V8 GC ASAP if system memory is pressured

base/memory/memory_pressure_listener.cc

Index: base/memory/memory_pressure_listener.cc
diff --git a/base/memory/memory_pressure_listener.cc b/base/memory/memory_pressure_listener.cc
index 11859ada613f77cd9418e87351d17c2f948589b2..de63958b929edf86bd61f54be7d5e387129157f3 100644
--- a/base/memory/memory_pressure_listener.cc
+++ b/base/memory/memory_pressure_listener.cc
@@ -12,48 +12,28 @@
 
 namespace {
 
-class MemoryPressureObserver {
- public:
-  MemoryPressureObserver()
-      : async_observers_(new ObserverListThreadSafe<MemoryPressureListener>),
-        sync_observers_(new ObserverList<MemoryPressureListener>) {
+// ObserverListThreadSafe is RefCountedThreadSafe, this traits is needed
+// to ensure the LazyInstance will hold a reference to it.
+struct LeakyLazyObserverListTraits :
+    base::internal::LeakyLazyInstanceTraits<
+        ObserverListThreadSafe<MemoryPressureListener> > {
+  static ObserverListThreadSafe<MemoryPressureListener>*
+      New(void* instance) {
+    ObserverListThreadSafe<MemoryPressureListener>* ret =
+        base::internal::LeakyLazyInstanceTraits<
+            ObserverListThreadSafe<MemoryPressureListener>>::New(instance);
+    // Leaky.
+    ret->AddRef();
+    return ret;
   }
-
-  void AddObserver(MemoryPressureListener* listener, bool sync) {
-    async_observers_->AddObserver(listener);
-    if (sync) {
-      AutoLock lock(sync_observers_lock_);
-      sync_observers_->AddObserver(listener);
-    }
-  }
-
-  void RemoveObserver(MemoryPressureListener* listener) {
-    async_observers_->RemoveObserver(listener);
-    AutoLock lock(sync_observers_lock_);
-    sync_observers_->RemoveObserver(listener);
-  }
-
-  void Notify(MemoryPressureListener::MemoryPressureLevel
-      memory_pressure_level) {
-    async_observers_->Notify(FROM_HERE,
-        &MemoryPressureListener::Notify, memory_pressure_level);
-    AutoLock lock(sync_observers_lock_);
-    FOR_EACH_OBSERVER(MemoryPressureListener, *sync_observers_,
-        MemoryPressureListener::SyncNotify(memory_pressure_level));
-  }
-
- private:
-  scoped_refptr<ObserverListThreadSafe<MemoryPressureListener>>
-      async_observers_;
-  ObserverList<MemoryPressureListener>* sync_observers_;
-  Lock sync_observers_lock_;
-
-  DISALLOW_COPY_AND_ASSIGN(MemoryPressureObserver);
 };
 
-LazyInstance<MemoryPressureObserver>::Leaky g_observer =
-    LAZY_INSTANCE_INITIALIZER;
+LazyInstance<
+    ObserverListThreadSafe<MemoryPressureListener>,
+    LeakyLazyObserverListTraits> g_observers = LAZY_INSTANCE_INITIALIZER;
 
+// All memory pressure notifications within this process will be suppressed if
+// this variable is set to 1.
 subtle::Atomic32 g_notifications_suppressed = 0;
 
 }  // namespace
@@ -61,31 +41,15 @@
 MemoryPressureListener::MemoryPressureListener(
     const MemoryPressureListener::MemoryPressureCallback& callback)
     : callback_(callback) {
-  g_observer.Get().AddObserver(this, false);
-}
-
-MemoryPressureListener::MemoryPressureListener(
-    const MemoryPressureListener::MemoryPressureCallback& callback,
-    const MemoryPressureListener::SyncMemoryPressureCallback&
-        sync_memory_pressure_callback)
-    : callback_(callback),
-      sync_memory_pressure_callback_(sync_memory_pressure_callback) {
-  g_observer.Get().AddObserver(this, true);
+  g_observers.Get().AddObserver(this);
 }
 
 MemoryPressureListener::~MemoryPressureListener() {
-  g_observer.Get().RemoveObserver(this);
+  g_observers.Get().RemoveObserver(this);
 }
 
 void MemoryPressureListener::Notify(MemoryPressureLevel memory_pressure_level) {
   callback_.Run(memory_pressure_level);
-}
-
-void MemoryPressureListener::SyncNotify(
-    MemoryPressureLevel memory_pressure_level) {
-  if (!sync_memory_pressure_callback_.is_null()) {
-    sync_memory_pressure_callback_.Run(memory_pressure_level);
-  }
 }
 
 // static
@@ -122,8 +86,8 @@
 void MemoryPressureListener::DoNotifyMemoryPressure(
     MemoryPressureLevel memory_pressure_level) {
   DCHECK_NE(memory_pressure_level, MEMORY_PRESSURE_LEVEL_NONE);
-
-  g_observer.Get().Notify(memory_pressure_level);
+  g_observers.Get().Notify(FROM_HERE, &MemoryPressureListener::Notify,
+                           memory_pressure_level);
 }
 
 }  // namespace base