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

components/plugins/renderer/webview_plugin.h

Index: components/plugins/renderer/webview_plugin.h
diff --git a/components/plugins/renderer/webview_plugin.h b/components/plugins/renderer/webview_plugin.h
index cfc991eed6d51cba7ac8d45fcefd8f466f8abbbb..cd91b617aac3d6b476b9673fe367f635ae1fb12a 100644
--- a/components/plugins/renderer/webview_plugin.h
+++ b/components/plugins/renderer/webview_plugin.h
@@ -109,13 +109,6 @@ class WebViewPlugin : public blink::WebPlugin,
   void didFinishLoading() override;
   void didFailLoading(const blink::WebURLError& error) override;
 
-  // Called in response to WebPluginContainer::loadFrameRequest
-  void didFinishLoadingFrameRequest(const blink::WebURL& url,
-                                    void* notifyData) override {}
-  void didFailLoadingFrameRequest(const blink::WebURL& url,
-                                  void* notify_data,
-                                  const blink::WebURLError& error) override {}
-
   // WebViewClient methods:
   bool acceptsLoadDrops() override;