Add MemoryPurgeController

Source/core/page/Page.cpp

Index: Source/core/page/Page.cpp
diff --git a/Source/core/page/Page.cpp b/Source/core/page/Page.cpp
index a453fd321a0baa67ebebef07214ffd734aa5682d..627cbab32074f6377e49a7cd043b22486cf5ef46 100644
--- a/Source/core/page/Page.cpp
+++ b/Source/core/page/Page.cpp
@@ -385,10 +385,13 @@ void Page::setVisibilityState(PageVisibilityState visibilityState, bool isInitia
         return;
     m_visibilityState = visibilityState;
 
-    if (visibilityState == PageVisibilityStateVisible)
+    if (visibilityState == PageVisibilityStateVisible) {
         setTimerAlignmentInterval(DOMTimer::visiblePageAlignmentInterval());
-    else
+        m_memoryPurgeController.pageBecameVisible();
+    } else {
         setTimerAlignmentInterval(DOMTimer::hiddenPageAlignmentInterval());
+        m_memoryPurgeController.pageBecameHidden();
+    }
 
     if (!isInitialState)
         notifyPageVisibilityChanged();
@@ -560,6 +563,7 @@ DEFINE_TRACE(Page)
     visitor->trace(m_frameHost);
     HeapSupplementable<Page>::trace(visitor);
 #endif
+    visitor->trace(m_memoryPurgeController);
     PageLifecycleNotifier::trace(visitor);
 }