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

third_party/WebKit/public/web/WebFrameClient.h

 /*
  * Copyright (C) 2011, 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 432 matching lines @@
 
     // A reflected XSS was encountered in the page and suppressed.
     virtual void didDetectXSS(const WebURL&, bool didBlockEntirePage) { }
 
     // A PingLoader was created, and a request dispatched to a URL.
     virtual void didDispatchPingLoader(WebLocalFrame*, const WebURL&) { }
 
     // A performance timing event (e.g. first paint) occurred
     virtual void didChangePerformanceTiming() { }
 
-    // The loaders in this frame have been stopped.
-    virtual void didAbortLoading(WebLocalFrame*) { }
-
 
     // Script notifications ------------------------------------------------
 
     // Notifies that a new script context has been created for this frame.
     // This is similar to didClearWindowObject but only called once per
     // frame context.
     virtual void didCreateScriptContext(WebLocalFrame*, v8::Local<v8::Context>, int extensionGroup, int worldId) { }
 
     // WebKit is about to release its reference to a v8 context for a frame.
     virtual void willReleaseScriptContext(WebLocalFrame*, v8::Local<v8::Context>, int worldId) { }
@@ skipping 222 matching lines @@
     // This method takes ownership of the callbacks pointer.
     virtual void checkIfAudioSinkExistsAndIsAuthorized(const WebString& sinkId, const WebSecurityOrigin&, WebSetSinkIdCallbacks*) { BLINK_ASSERT_NOT_REACHED(); }
 
 protected:
     virtual ~WebFrameClient() { }
 };
 
 } // namespace blink
 
 #endif