Apply artificial memory pressure when backgrounded.

In https://codereview.chromium.org/17106004/, I am adding discardable memory
emulation for platforms that do not support it natively. The emulation works by
listening for memory pressure notifications and purging memory in response.
But we don't yet provide memory pressure notifications on any platform other
than android.

In future, we'll periodically poll system memory usage, and send memory pressure
notifications as appropriate, but as a first step, we will artificially apply
memory pressure when tabs are backgrounded.

BUG=237681

Review URL: https://chromiumcodereview.appspot.com/17355004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@207947 0039d316-1c4b-4281-b951-d872f2087c98

content/content_renderer.gypi

@@ -278,6 +278,8 @@
     'renderer/render_process.h',
     'renderer/render_process_impl.cc',
     'renderer/render_process_impl.h',
+    'renderer/render_process_visibility_manager.cc',
+    'renderer/render_process_visibility_manager.h',
     'renderer/render_thread_impl.cc',
     'renderer/render_thread_impl.h',
     'renderer/render_view_impl.cc',

content/renderer/render_process_visibility_manager.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 "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

content/renderer/render_process_visibility_manager.h

+// 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.
+
+#ifndef CONTENT_RENDERER_RENDER_PROCESS_VISIBILITY_MANAGER_H_
+#define CONTENT_RENDERER_RENDER_PROCESS_VISIBILITY_MANAGER_H_
+
+#include "base/memory/singleton.h"
+#include "content/common/content_export.h"
+
+namespace content {
+
+class CONTENT_EXPORT RenderProcessVisibilityManager {
+ public:
+  static RenderProcessVisibilityManager* GetInstance();
+
+  void WidgetVisibilityChanged(bool visible);
+
+ private:
+  friend struct DefaultSingletonTraits<RenderProcessVisibilityManager>;
+
+  RenderProcessVisibilityManager();
+  ~RenderProcessVisibilityManager();
+
+  int num_visible_render_widgets_;
+
+  DISALLOW_COPY_AND_ASSIGN(RenderProcessVisibilityManager);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_RENDERER_RENDER_PROCESS_VISIBILITY_MANAGER_H_

content/renderer/render_thread_impl.cc

@@ -14,6 +14,7 @@
 #include "base/debug/trace_event.h"
 #include "base/lazy_instance.h"
 #include "base/logging.h"
+#include "base/memory/discardable_memory.h"
 #include "base/metrics/field_trial.h"
 #include "base/metrics/histogram.h"
 #include "base/metrics/stats_table.h"
@@ -71,6 +72,7 @@
 #include "content/renderer/p2p/socket_dispatcher.h"
 #include "content/renderer/plugin_channel_host.h"
 #include "content/renderer/render_process_impl.h"
+#include "content/renderer/render_process_visibility_manager.h"
 #include "content/renderer/render_view_impl.h"
 #include "content/renderer/renderer_webkitplatformsupport_impl.h"
 #include "content/renderer/skia_benchmarking_extension.h"
@@ -597,6 +599,10 @@ void RenderThreadImpl::WidgetHidden() {
   DCHECK(hidden_widget_count_ < widget_count_);
   hidden_widget_count_++;
 
+  RenderProcessVisibilityManager* manager =
+      RenderProcessVisibilityManager::GetInstance();
+  manager->WidgetVisibilityChanged(false);
+
   if (!GetContentClient()->renderer()->RunIdleHandlerWhenWidgetsHidden()) {
     return;
   }
@@ -608,6 +614,11 @@ void RenderThreadImpl::WidgetHidden() {
 void RenderThreadImpl::WidgetRestored() {
   DCHECK_GT(hidden_widget_count_, 0);
   hidden_widget_count_--;
+
+  RenderProcessVisibilityManager* manager =
+      RenderProcessVisibilityManager::GetInstance();
+  manager->WidgetVisibilityChanged(true);
+
   if (!GetContentClient()->renderer()->RunIdleHandlerWhenWidgetsHidden()) {
     return;
   }

content/renderer/render_widget.cc

@@ -30,6 +30,7 @@
 #include "content/renderer/gpu/render_widget_compositor.h"
 #include "content/renderer/ime_event_guard.h"
 #include "content/renderer/render_process.h"
+#include "content/renderer/render_process_visibility_manager.h"
 #include "content/renderer/render_thread_impl.h"
 #include "content/renderer/renderer_webkitplatformsupport_impl.h"
 #include "ipc/ipc_sync_message.h"
@@ -188,6 +189,8 @@ RenderWidget::RenderWidget(WebKit::WebPopupType popup_type,
   is_threaded_compositing_enabled_ =
       CommandLine::ForCurrentProcess()->HasSwitch(
           switches::kEnableThreadedCompositing);
+
+  RenderProcessVisibilityManager::GetInstance()->WidgetVisibilityChanged(true);
 }
 
 RenderWidget::~RenderWidget() {