Explicitly cut link between WebViewPlugin and PluginPlaceholder

components/plugins/renderer/plugin_placeholder.cc

Index: components/plugins/renderer/plugin_placeholder.cc
diff --git a/components/plugins/renderer/plugin_placeholder.cc b/components/plugins/renderer/plugin_placeholder.cc
index f99ee489fb6de122f4533dfe261fc63e682ab083..14aff7023fce2a53ae506736fe8e47e5c571d836 100644
--- a/components/plugins/renderer/plugin_placeholder.cc
+++ b/components/plugins/renderer/plugin_placeholder.cc
@@ -88,7 +88,6 @@ void PluginPlaceholder::ReplacePlugin(WebPlugin* new_plugin) {
   // will be destroyed as soon as V8 garbage collects us.
   if (!element.pluginContainer()) {
     plugin_->destroy();
-    plugin_ = NULL;
     return;
   }
 
@@ -102,7 +101,6 @@ void PluginPlaceholder::ReplacePlugin(WebPlugin* new_plugin) {
   container->reportGeometry();
   plugin_->ReplayReceivedData(new_plugin);
   plugin_->destroy();
-  plugin_ = NULL;
 }
 
 void PluginPlaceholder::HidePlugin() {
@@ -174,6 +172,10 @@ void PluginPlaceholder::ShowContextMenu(const WebMouseEvent& event) {
   return;
 }
 
+void PluginPlaceholder::PluginDestroyed() {
+  plugin_ = NULL;
+}
+
 void PluginPlaceholder::OnDestruct() {
   frame_ = NULL;
 }