Remove PluginLoadObserver and related logic, it was only used for NPAPI.

third_party/WebKit/public/web/WebPluginContainer.h

Index: third_party/WebKit/public/web/WebPluginContainer.h
diff --git a/third_party/WebKit/public/web/WebPluginContainer.h b/third_party/WebKit/public/web/WebPluginContainer.h
index b757702073351c13e9cdcb827a1c5bcc9257254b..46edc00fcefa3c2c015f2c076097acb952a9c9eb 100644
--- a/third_party/WebKit/public/web/WebPluginContainer.h
+++ b/third_party/WebKit/public/web/WebPluginContainer.h
@@ -106,7 +106,7 @@ public:
     // called if the load failed.  The given notifyData is passed along to
     // the callback.
     virtual void loadFrameRequest(
-        const WebURLRequest&, const WebString& target, bool notifyNeeded, void* notifyData) = 0;
+        const WebURLRequest&, const WebString& target) = 0;
 
     // Determines whether the given rectangle in this plugin is above all other
     // content. The rectangle is in the plugin's coordinate system.