Persist plugins over reattach.

Source/web/WebPluginContainerImpl.cpp

Index: Source/web/WebPluginContainerImpl.cpp
diff --git a/Source/web/WebPluginContainerImpl.cpp b/Source/web/WebPluginContainerImpl.cpp
index 6196f7769f4d8f07eb1aaa7f0712a0751f822b2f..8ec7ca5205cc8375c766985d4722f1946bcfa66f 100644
--- a/Source/web/WebPluginContainerImpl.cpp
+++ b/Source/web/WebPluginContainerImpl.cpp
@@ -244,7 +244,8 @@ void WebPluginContainerImpl::setParentVisible(bool parentVisible)
     if (!isSelfVisible())
         return;  // This widget has explicitely been marked as not visible.
 
-    m_webPlugin->updateVisibility(isVisible());
+    if (m_webPlugin)
+        m_webPlugin->updateVisibility(isVisible());
 }
 
 void WebPluginContainerImpl::setParent(Widget* widget)
@@ -710,11 +711,14 @@ void WebPluginContainerImpl::dispose()
     for (size_t i = 0; i < m_pluginLoadObservers.size(); ++i)
         m_pluginLoadObservers[i]->clearPluginContainer();
 
-    m_webPlugin->destroy();
+    if (m_webPlugin)
+        m_webPlugin->destroy();
     m_webPlugin = nullptr;
 
-    if (m_webLayer)
+    if (m_webLayer) {
         GraphicsLayer::unregisterContentsLayer(m_webLayer);
+        m_webLayer = nullptr;
+    }
 
     m_pluginLoadObservers.clear();
     m_element = nullptr;
@@ -953,9 +957,4 @@ void WebPluginContainerImpl::calculateGeometry(IntRect& windowRect, IntRect& cli
         cutOutRects[i].move(-frameRect().x(), -frameRect().y());
 }
 
-bool WebPluginContainerImpl::pluginShouldPersist() const
-{
-    return m_webPlugin->shouldPersist();
-}
-
 } // namespace blink