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

content/renderer/npapi/webplugin_delegate_proxy.h

Index: content/renderer/npapi/webplugin_delegate_proxy.h
diff --git a/content/renderer/npapi/webplugin_delegate_proxy.h b/content/renderer/npapi/webplugin_delegate_proxy.h
index 2d770eeaea810953135555e7c2b3032000ca44e8..b5688eecdef713a9953c62aaf47de3bf73a3fdfd 100644
--- a/content/renderer/npapi/webplugin_delegate_proxy.h
+++ b/content/renderer/npapi/webplugin_delegate_proxy.h
@@ -68,9 +68,6 @@ class WebPluginDelegateProxy
   NPObject* GetPluginScriptableObject() override;
   struct _NPP* GetPluginNPP() override;
   bool GetFormValue(base::string16* value) override;
-  void DidFinishLoadWithReason(const GURL& url,
-                               NPReason reason,
-                               int notify_id) override;
   void SetFocus(bool focused) override;
   bool HandleInputEvent(const blink::WebInputEvent& event,
                         WebCursor::CursorInfo* cursor) override;
@@ -114,8 +111,7 @@ class WebPluginDelegateProxy
 
   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,
@@ -126,13 +122,11 @@ class WebPluginDelegateProxy
   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,