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

content/renderer/render_frame_impl.cc

Index: content/renderer/render_frame_impl.cc
diff --git a/content/renderer/render_frame_impl.cc b/content/renderer/render_frame_impl.cc
index 0db8f24e912c0fabcddef7f30b37c8e696090b5a..76dd11c5c9a615c5cffb180597bdd914503f8e02 100644
--- a/content/renderer/render_frame_impl.cc
+++ b/content/renderer/render_frame_impl.cc
@@ -3723,16 +3723,6 @@ void RenderFrameImpl::didChangePerformanceTiming() {
                     DidChangePerformanceTiming());
 }
 
-void RenderFrameImpl::didAbortLoading(blink::WebLocalFrame* frame) {
-  DCHECK(!frame_ || frame_ == frame);
-#if defined(ENABLE_PLUGINS)
-  if (frame != render_view_->webview()->mainFrame())
-    return;
-  PluginChannelHost::Broadcast(
-      new PluginHostMsg_DidAbortLoading(render_view_->GetRoutingID()));
-#endif
-}
-
 void RenderFrameImpl::didCreateScriptContext(blink::WebLocalFrame* frame,
                                              v8::Local<v8::Context> context,
                                              int extension_group,