Adds MemoryPressureListener.

Some platforms, like android, send clear signals when
under memory pressure.
Create a centralized place so that:
- Underlying platform can advise the rest of the system of
its memory status.
- Individual subsystems can then listen to such notifications
and free their memory as per their own policies.

BUG=246125

Review URL: https://chromiumcodereview.appspot.com/15995014

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@205796 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 40 insertions, 0 deletions

diff --git a/base/memory/memory_pressure_listener.cc b/base/memory/memory_pressure_listener.cc
new file mode 100644
index 0000000..911dbb3
--- /dev/null
+++ b/base/memory/memory_pressure_listener.cc
@@ -0,0 +1,40 @@
+// 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"
+
+namespace {
+
+base::LazyInstance<ObserverListThreadSafe<base::MemoryPressureListener> >::Leaky
+    g_observers = LAZY_INSTANCE_INITIALIZER;
+
+}  // namespace
+
+namespace base {
+
+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) {
+  g_observers.Get().Notify(&MemoryPressureListener::Notify,
+                           memory_pressure_level);
+}
+
+}  // namespace base