Move plugin placeholder style to CSS, and allow it to bypass main world CSP.

Source/core/core.gypi

 {
     'includes': [
       'core_generated.gypi',
     ],
     'variables': {
         # Files for which bindings (.cpp and .h files) will be generated
         'core_idl_files': [
             'animation/Animation.idl',
             'animation/AnimationEffect.idl',
             'animation/AnimationPlayer.idl',
@@ skipping 463 matching lines @@
             'dom/URLUtils.idl',
             'dom/URLUtilsReadOnly.idl',
             'events/EventListener.idl',
             'events/NavigatorEvents.idl',
             'frame/NavigatorCPU.idl',
             'frame/NavigatorID.idl',
             'frame/NavigatorLanguage.idl',
             'frame/NavigatorOnLine.idl',
             'frame/WindowBase64.idl',
             'frame/WindowEventHandlers.idl',
+            'frame/WindowPrivateScript.idl',
             'frame/WindowTimers.idl',
             'html/canvas/CanvasPathMethods.idl',
             'html/canvas/MouseEventHitRegion.idl',
             'html/canvas/WebGLRenderingContextBase.idl',
             'imagebitmap/ImageBitmapFactories.idl',
             'imagebitmap/WindowImageBitmapFactories.idl',
             'page/WindowPagePopup.idl',
             'svg/SVGDocument.idl',
             'svg/SVGFilterPrimitiveStandardAttributes.idl',
             'svg/SVGFitToViewBox.idl',
@@ skipping 657 matching lines @@
             'frame/ConsoleBase.h',
             'frame/DOMTimer.cpp',
             'frame/DOMTimer.h',
             'frame/DOMWindowBase64.cpp',
             'frame/DOMWindowBase64.h',
             'frame/DOMWindowEventHandlers.h',
             'frame/DOMWindowLifecycleNotifier.cpp',
             'frame/DOMWindowLifecycleNotifier.h',
             'frame/DOMWindowLifecycleObserver.cpp',
             'frame/DOMWindowLifecycleObserver.h',
+            'frame/DOMWindowPrivateScript.cpp',
+            'frame/DOMWindowPrivateScript.h',
             'frame/DOMWindowProperty.cpp',
             'frame/DOMWindowProperty.h',
             'frame/DOMWindowTimers.cpp',
             'frame/DOMWindowTimers.h',
             'frame/DeprecatedScheduleStyleRecalcDuringLayout.cpp',
             'frame/DeprecatedScheduleStyleRecalcDuringLayout.h',
             'frame/DeviceSingleWindowEventController.cpp',
             'frame/DeviceSingleWindowEventController.h',
             'frame/EventHandlerRegistry.cpp',
             'frame/EventHandlerRegistry.h',
@@ skipping 2350 matching lines @@
             'rendering/shapes/BoxShapeTest.cpp',
             'rendering/style/OutlineValueTest.cpp',
             'testing/PrivateScriptTestTest.cpp',
             'streams/ReadableStreamTest.cpp',
             'testing/UnitTestHelpers.cpp',
             'testing/UnitTestHelpers.h',
             'xml/parser/SharedBufferReaderTest.cpp',
         ],
     }
 }