Blink Plugins: Remove Shadow DOM Plugin Placeholder remnants.

Source/core/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/chrome_build.gni")
 import("//build/config/ui.gni")
 import("//third_party/WebKit/Source/bindings/bindings.gni")
 import("//third_party/WebKit/Source/bindings/core/v8/generated.gni")
 import("//third_party/WebKit/Source/bindings/modules/modules.gni")
 import("//third_party/WebKit/Source/bindings/modules/v8/generated.gni")
@@ skipping 327 matching lines @@
     "$bindings_core_v8_output_dir/V8LayerRect.cpp",
     "$bindings_core_v8_output_dir/V8LayerRect.h",
     "$bindings_core_v8_output_dir/V8LayerRectList.cpp",
     "$bindings_core_v8_output_dir/V8LayerRectList.h",
     "$bindings_core_v8_output_dir/V8RefCountedScriptWrappable.cpp",
     "$bindings_core_v8_output_dir/V8RefCountedScriptWrappable.h",
     "$bindings_core_v8_output_dir/V8InternalDictionary.cpp",
     "$bindings_core_v8_output_dir/V8InternalDictionary.h",
     "$bindings_core_v8_output_dir/V8InternalDictionaryDerived.cpp",
     "$bindings_core_v8_output_dir/V8InternalDictionaryDerived.h",
-    "$bindings_core_v8_output_dir/V8PluginPlaceholderOptions.cpp",
-    "$bindings_core_v8_output_dir/V8PluginPlaceholderOptions.h",
   ]
 }
 
 # GYP version: //third_party/WebKit/Source/core/core.gyp:webcore_generated
 source_set("core_generated") {
   sources = bindings_core_v8_files
   # These files include all the .cpp files generated from the .idl files
   # in webcore_files.
   sources += bindings_core_generated_aggregate_files
   sources += bindings_core_generated_union_type_files
@@ skipping 680 matching lines @@
     "$blink_core_output_dir/{{source_name_part}}.h",
   ]
   args = [
     "{{source}}",
     rel_blink_core_gen_dir,
     bison_exe,
   ]
 
   deps = make_core_generated_deps
 }