Move PlatformEventDispatcher implementations to the Oilpan heap.

Source/core/frame/PlatformEventDispatcher.cpp

Index: Source/core/frame/PlatformEventDispatcher.cpp
diff --git a/Source/core/frame/PlatformEventDispatcher.cpp b/Source/core/frame/PlatformEventDispatcher.cpp
index 397d7881752d3dd435ddd6410d8a191368f72f71..5ed4d87af28dcbcb787c21c39ce6249fe219e0f9 100644
--- a/Source/core/frame/PlatformEventDispatcher.cpp
+++ b/Source/core/frame/PlatformEventDispatcher.cpp
@@ -16,10 +16,6 @@ PlatformEventDispatcher::PlatformEventDispatcher()
 {
 }
 
-PlatformEventDispatcher::~PlatformEventDispatcher()
-{
-}
-
 void PlatformEventDispatcher::addController(PlatformEventController* controller)
 {
     bool wasEmpty = m_controllers.isEmpty();
@@ -84,4 +80,21 @@ void PlatformEventDispatcher::notifyControllers()
         purgeControllers();
 }
 
+void PlatformEventDispatcher::trace(Visitor* visitor)
+{
+    visitor->trace(m_controllers);
+    visitor->registerWeakMembers<PlatformEventDispatcher, &PlatformEventDispatcher::clearWeakMembers>(this);
+}
+
+void PlatformEventDispatcher::clearWeakMembers(Visitor* visitor)
+{
+    for (size_t i = 0; i < m_controllers.size(); ++i) {
+        if (!visitor->isAlive(m_controllers[i])) {
+            m_controllers[i] = nullptr;
+            m_needsPurge = true;
+        }
+    }
+    // Next notification will purge the empty slots.
+}
+
 } // namespace blink