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

content/child/npapi/webplugin_delegate_impl.h

Index: content/child/npapi/webplugin_delegate_impl.h
diff --git a/content/child/npapi/webplugin_delegate_impl.h b/content/child/npapi/webplugin_delegate_impl.h
index 72f559a9b1dd286edc1d57aeef70286e64bf62ab..8535d2343e35628794969f1539e019a03b6da828 100644
--- a/content/child/npapi/webplugin_delegate_impl.h
+++ b/content/child/npapi/webplugin_delegate_impl.h
@@ -92,14 +92,10 @@ class WebPluginDelegateImpl : public WebPluginDelegate {
   NPObject* GetPluginScriptableObject() override;
   NPP GetPluginNPP() override;
   bool GetFormValue(base::string16* value) override;
-  void DidFinishLoadWithReason(const GURL& url,
-                               NPReason reason,
-                               int notify_id) override;
   int GetProcessId() override;
   void SendJavaScriptStream(const GURL& url,
                             const std::string& result,
-                            bool success,
-                            int notify_id) override;
+                            bool success) override;
   void DidReceiveManualResponse(const GURL& url,
                                 const std::string& mime_type,
                                 const std::string& headers,
@@ -109,13 +105,11 @@ class WebPluginDelegateImpl : public WebPluginDelegate {
   void DidFinishManualLoading() override;
   void DidManualLoadFail() override;
   WebPluginResourceClient* CreateResourceClient(unsigned long resource_id,
-                                                const GURL& url,
-                                                int notify_id) override;
+                                                const GURL& url) override;
   WebPluginResourceClient* CreateSeekableResourceClient(
       unsigned long resource_id,
       int range_request_id) override;
   void FetchURL(unsigned long resource_id,
-                int notify_id,
                 const GURL& url,
                 const GURL& first_party_for_cookies,
                 const std::string& method,