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

third_party/WebKit/Source/web/FrameLoaderClientImpl.h

Index: third_party/WebKit/Source/web/FrameLoaderClientImpl.h
diff --git a/third_party/WebKit/Source/web/FrameLoaderClientImpl.h b/third_party/WebKit/Source/web/FrameLoaderClientImpl.h
index 3cdeabc448f7e672b6e4b16aa98aff475bbde180..360f5b00fd1d8a9cc50ac60906ab222ad6bf21d4 100644
--- a/third_party/WebKit/Source/web/FrameLoaderClientImpl.h
+++ b/third_party/WebKit/Source/web/FrameLoaderClientImpl.h
@@ -41,7 +41,6 @@
 namespace blink {
 
 class WebLocalFrameImpl;
-class WebPluginLoadObserver;
 
 class FrameLoaderClientImpl final : public FrameLoaderClient {
 public:
@@ -171,8 +170,6 @@ public:
 
     PassOwnPtr<WebApplicationCacheHost> createApplicationCacheHost(WebApplicationCacheHostClient*) override;
 
-    void didStopAllLoaders() override;
-
     void dispatchDidChangeManifest() override;
 
     unsigned backForwardLength() override;
@@ -184,8 +181,6 @@ private:
 
     bool isFrameLoaderClientImpl() const override { return true; }
 
-    PassOwnPtrWillBeRawPtr<WebPluginLoadObserver> pluginLoadObserver(DocumentLoader*);
-
     // The WebFrame that owns this object and manages its lifetime. Therefore,
     // the web frame object is guaranteed to exist.
     RawPtrWillBeMember<WebLocalFrameImpl> m_webFrame;