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

content/child/BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
 import("//content/child/child.gni")
 
 source_set("child") {
   # Only the public target should depend on this. All other targets (even
@@ skipping 54 matching lines @@
     }
   } else {
     sources -= [
       "browser_font_resource_trusted.cc",
       "npapi/plugin_host.cc",
       "npapi/plugin_host.h",
       "npapi/plugin_instance.cc",
       "npapi/plugin_instance.h",
       "npapi/plugin_lib.cc",
       "npapi/plugin_lib.h",
-      "npapi/plugin_stream.cc",
-      "npapi/plugin_stream.h",
-      "npapi/plugin_stream_posix.cc",
-      "npapi/plugin_stream_url.cc",
-      "npapi/plugin_stream_url.h",
-      "npapi/plugin_string_stream.cc",
-      "npapi/plugin_string_stream.h",
-      "npapi/plugin_url_fetcher.cc",
-      "npapi/plugin_url_fetcher.h",
       "npapi/webplugin.h",
       "npapi/webplugin_delegate.h",
       "npapi/webplugin_delegate_impl.cc",
       "npapi/webplugin_delegate_impl.h",
       "npapi/webplugin_resource_client.h",
     ]
 
     if (is_mac) {
       sources -= [
         "npapi/plugin_instance_mac.mm",
         "npapi/plugin_web_event_converter_mac.h",
         "npapi/plugin_web_event_converter_mac.mm",
         "npapi/webplugin_accelerated_surface_mac.h",
         "npapi/webplugin_delegate_impl_mac.mm",
       ]
     } else if (is_win) {
       sources -= [
-        "npapi/plugin_stream_win.cc",
         "npapi/webplugin_delegate_impl_win.cc",
         "npapi/webplugin_ime_win.cc",
         "npapi/webplugin_ime_win.h",
       ]
     } else if (is_android) {
       sources -= [ "npapi/webplugin_delegate_impl_android.cc" ]
     }
     sources -= [ "npapi/webplugin_delegate_impl_aura.cc" ]
   }
 
@@ skipping 18 matching lines @@
       "//third_party/WebKit/public:resources",
       "//third_party/npapi",
     ]
   }
 
   if (use_aura && is_mac) {
     # This file is already excluded on non-Mac.
     sources -= [ "npapi/webplugin_delegate_impl_mac.mm" ]
   }
 }