Add MemoryPurgeController

No client so far. Follow-up CLs will add actual clients.

Design doc:
https://docs.google.com/document/d/1TbtkhXpjw_8lftLwELuEPEgcyWfXuVLuqW2KYJZeaBA/edit?pli=1

Non trivial changes from the design doc:
- MemoryPurgeController owns its clients.
- Page owns MemoryPurgeController (because core/ and modules/ will want
  to access MemoryPurgeController to register clients)

I chose Page as the owner of the controller because it has the same
lifetime of WebView.

BUG=520496

Review URL: https://codereview.chromium.org/1303203002

git-svn-id: svn://svn.chromium.org/blink/trunk@201116 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/core/page/Page.cpp

@@ -560,6 +560,7 @@ DEFINE_TRACE(Page)
     visitor->trace(m_frameHost);
     HeapSupplementable<Page>::trace(visitor);
 #endif
+    visitor->trace(m_memoryPurgeController);
     PageLifecycleNotifier::trace(visitor);
 }
 

third_party/WebKit/Source/core/page/Page.h

@@ -32,6 +32,7 @@
 #include "core/page/PageLifecycleNotifier.h"
 #include "core/page/PageLifecycleObserver.h"
 #include "core/page/PageVisibilityState.h"
+#include "platform/MemoryPurgeController.h"
 #include "platform/Supplementable.h"
 #include "platform/geometry/LayoutRect.h"
 #include "platform/geometry/Region.h"
@@ -204,6 +205,8 @@ public:
 
     static void networkStateChanged(bool online);
 
+    MemoryPurgeController& memoryPurgeController() { return m_memoryPurgeController; }
+
     DECLARE_TRACE();
     void willBeDestroyed();
 
@@ -273,6 +276,8 @@ private:
     // A pointer to all the interfaces provided to in-process Frames for this Page.
     // FIXME: Most of the members of Page should move onto FrameHost.
     OwnPtrWillBeMember<FrameHost> m_frameHost;
+
+    MemoryPurgeController m_memoryPurgeController;
 };
 
 extern template class CORE_EXTERN_TEMPLATE_EXPORT WillBeHeapSupplement<Page>;

third_party/WebKit/Source/platform/MemoryPurgeController.cpp

+// Copyright 2015 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 "config.h"
+#include "platform/MemoryPurgeController.h"
+
+#include "public/platform/Platform.h"
+
+namespace blink {
+
+MemoryPurgeController::MemoryPurgeController()
+    : m_deviceKind(Platform::current()->isLowEndDeviceMode() ? DeviceKind::LowEnd : DeviceKind::NotSpecified)
+{
+}
+
+void MemoryPurgeController::purgeMemory(MemoryPurgeMode purgeMode)
+{
+    for (auto& client : m_clients)
+        client->purgeMemory(purgeMode, m_deviceKind);
+}
+
+DEFINE_TRACE(MemoryPurgeController)
+{
+#if ENABLE(OILPAN)
+    visitor->trace(m_clients);
+#endif
+}
+
+} // namespace blink

third_party/WebKit/Source/platform/MemoryPurgeController.h

+// Copyright 2015 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 MemoryPurgeController_h
+#define MemoryPurgeController_h
+
+#include "platform/PlatformExport.h"
+#include "platform/heap/Handle.h"
+#include "wtf/MainThread.h"
+
+namespace blink {
+
+enum class MemoryPurgeMode {
+    // The tab contains the webview went to background
+    InactiveTab,
+    // TODO(bashi): Add more modes as needed.
+};
+
+enum class DeviceKind {
+    NotSpecified,
+    LowEnd,
+};
+
+// Classes which have discardable/reducible memory can implement this
+// interface to be informed when they should reduce memory consumption.
+// MemoryPurgeController assumes that subclasses of MemoryPurgeClient are
+// WillBes.
+class MemoryPurgeClient : public WillBeGarbageCollectedMixin {
+public:
+    virtual ~MemoryPurgeClient() { }
+
+    // MemoryPurgeController invokes this callback when a memory purge event
+    // has occurred.
+    virtual void purgeMemory(MemoryPurgeMode, DeviceKind) = 0;
+
+    DECLARE_TRACE();
+};
+
+// MemoryPurgeController listens to some events which could be opportunities
+// for reducing memory consumption and notifies its clients.
+// Since we want to control memory per tab, MemoryPurgeController is owned by
+// Page.
+class PLATFORM_EXPORT MemoryPurgeController {
+public:
+    MemoryPurgeController();
+
+    void registerClient(MemoryPurgeClient* client)
+    {
+        ASSERT(isMainThread());
+        ASSERT(client);
+        ASSERT(!m_clients.contains(client));
+        m_clients.add(client);
+    }
+
+    void unregisterClient(MemoryPurgeClient* client)
+    {
+        ASSERT(isMainThread());
+        ASSERT(m_clients.contains(client));
+        m_clients.remove(client);
+    }
+
+    DECLARE_TRACE();
+
+private:
+    void purgeMemory(MemoryPurgeMode);
+
+    WillBeHeapHashSet<RawPtrWillBeWeakMember<MemoryPurgeClient>> m_clients;
+    DeviceKind m_deviceKind;
+};
+
+} // namespace blink
+
+#endif // MemoryPurgeController_h

third_party/WebKit/Source/platform/blink_platform.gypi

@@ -70,6 +70,8 @@
       'MIMETypeFromURL.h',
       'MIMETypeRegistry.cpp',
       'MIMETypeRegistry.h',
+      'MemoryPurgeController.cpp',
+      'MemoryPurgeController.h',
       'NotImplemented.cpp',
       'NotImplemented.h',
       'PartitionAllocMemoryDumpProvider.cpp',