[Not for review] Discardable memory emulation

content/renderer/render_process_visibility_manager.cc

+// Copyright (c) 2012 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 "content/renderer/render_process_visibility_manager.h"
+
+namespace content {
+
+RenderProcessVisibilityManager::RenderProcessVisibilityManager()
+    : num_visible_render_widgets_(0) {
+}
+
+RenderProcessVisibilityManager::~RenderProcessVisibilityManager() {
+}
+
+// static
+RenderProcessVisibilityManager* RenderProcessVisibilityManager::GetInstance() {
+  return Singleton<RenderProcessVisibilityManager>::get();
+}
+
+void RenderProcessVisibilityManager::WidgetVisibilityChanged(bool visible) {
+  const int old_num_visible_render_widgets = num_visible_render_widgets_;
+  num_visible_render_widgets_ += visible ? 1 : -1;
+  DCHECK_LE(0, num_visible_render_widgets_);
+
+  if (old_num_visible_render_widgets == 0)
+    FOR_EACH_OBSERVER(RenderProcessVisibilityObserver,
+                      observers_,
+                      RenderProcessVisibilityChanged(true));
+  if (num_visible_render_widgets_ == 0)
+    FOR_EACH_OBSERVER(RenderProcessVisibilityObserver,
+                      observers_,
+                      RenderProcessVisibilityChanged(false));
+}
+
+void RenderProcessVisibilityManager::AddObserver(
+    RenderProcessVisibilityObserver* observer) {
+  observers_.AddObserver(observer);
+}
+
+void RenderProcessVisibilityManager::RemoveObserver(
+    RenderProcessVisibilityObserver* observer) {
+  observers_.RemoveObserver(observer);
+}
+
+}  // namespace content