Add method for suppressing MemoryPressureListener notifications

base/memory/memory_pressure_listener.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/memory/memory_pressure_listener.h"
 
 #include "base/lazy_instance.h"
 #include "base/observer_list_threadsafe.h"
 #include "base/trace_event/trace_event.h"
 
@@ skipping 14 matching lines @@
     // Leaky.
     ret->AddRef();
     return ret;
   }
 };
 
 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
 
 MemoryPressureListener::MemoryPressureListener(
     const MemoryPressureListener::MemoryPressureCallback& callback)
     : callback_(callback) {
   g_observers.Get().AddObserver(this);
 }
 
 MemoryPressureListener::~MemoryPressureListener() {
   g_observers.Get().RemoveObserver(this);
 }
 
 void MemoryPressureListener::Notify(MemoryPressureLevel memory_pressure_level) {
   callback_.Run(memory_pressure_level);
 }
 
 // static
 void MemoryPressureListener::NotifyMemoryPressure(
     MemoryPressureLevel memory_pressure_level) {
   DCHECK_NE(memory_pressure_level, MEMORY_PRESSURE_LEVEL_NONE);
   TRACE_EVENT1("memory", "MemoryPressureListener::NotifyMemoryPressure",
       "level", memory_pressure_level);
+  if (AreNotificationsSuppressed())
+    return;
   g_observers.Get().Notify(FROM_HERE, &MemoryPressureListener::Notify,
                            memory_pressure_level);
 }
 
+// static
+bool MemoryPressureListener::AreNotificationsSuppressed() {
+  return subtle::Acquire_Load(&g_notifications_suppressed) == 1;
+}
+
+// static
+void MemoryPressureListener::SetNotificationsSuppressed(bool suppress) {
+  subtle::Release_Store(&g_notifications_suppressed, suppress ? 1 : 0);
+}
+
 }  // namespace base