Apply artificial memory pressure when backgrounded.

content/renderer/render_process_visibility_manager.cc

Index: content/renderer/render_process_visibility_manager.cc
diff --git a/content/renderer/render_process_visibility_manager.cc b/content/renderer/render_process_visibility_manager.cc
new file mode 100644
index 0000000000000000000000000000000000000000..8231df4552174355793983775a2c2e2bbd025ecc
--- /dev/null
+++ b/content/renderer/render_process_visibility_manager.cc
@@ -0,0 +1,37 @@
+// 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 "content/renderer/render_process_visibility_manager.h"
+
+#include "base/logging.h"
+#include "base/memory/memory_pressure_listener.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) {
+#if !defined(DISCARDABLE_MEMORY_ALWAYS_SUPPORTED_NATIVELY)
+  num_visible_render_widgets_ += visible ? 1 : -1;
+  DCHECK_LE(0, num_visible_render_widgets_);
+  if (num_visible_render_widgets_ == 0) {
+    // TODO(vollick): Remove this this heavy-handed approach once we're polling
+    // the real system memory pressure.
+    base::MemoryPressureListener::NotifyMemoryPressure(
+        base::MemoryPressureListener::MEMORY_PRESSURE_CRITICAL);
+  }
+#endif
+}
+
+}  // namespace content