Move BrowserPluginDelegate's lifetime mgmt out of content/

content/public/renderer/browser_plugin_delegate.h

Index: content/public/renderer/browser_plugin_delegate.h
diff --git a/content/public/renderer/browser_plugin_delegate.h b/content/public/renderer/browser_plugin_delegate.h
index 583c43c4bcddcd6ed0a05654647805fdf5f19f0a..e2ea5ca58ede9c8675c6760d03779aeed53d182a 100644
--- a/content/public/renderer/browser_plugin_delegate.h
+++ b/content/public/renderer/browser_plugin_delegate.h
@@ -47,6 +47,9 @@ class CONTENT_EXPORT BrowserPluginDelegate {
   // Called when the plugin resizes.
   virtual void DidResizeElement(const gfx::Size& new_size) {}
 
+  // Called when the plugin is about to be destroyed.
+  virtual void WillDestroy() {}
+
   // Return a scriptable object for the plugin.
   virtual v8::Local<v8::Object> V8ScriptableObject(v8::Isolate* isolate);
 };