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

Source/core/frame/LocalDOMWindow.h

Index: Source/core/frame/LocalDOMWindow.h
diff --git a/Source/core/frame/LocalDOMWindow.h b/Source/core/frame/LocalDOMWindow.h
index 9f6157a9194838927cfec04abac7fc53b9a4e848..650f5485582ea913b7dba069b08f4b9080cd58e2 100644
--- a/Source/core/frame/LocalDOMWindow.h
+++ b/Source/core/frame/LocalDOMWindow.h
@@ -30,6 +30,7 @@
 #include "bindings/core/v8/Dictionary.h"
 #include "core/events/EventTarget.h"
 #include "core/frame/DOMWindowBase64.h"
+#include "core/frame/DOMWindowPrivateScript.h"
 #include "core/frame/FrameDestructionObserver.h"
 #include "platform/LifecycleContext.h"
 #include "platform/Supplementable.h"
@@ -92,7 +93,7 @@ enum PageshowEventPersistence {
 
 enum SetLocationLocking { LockHistoryBasedOnGestureState, LockHistoryAndBackForwardList };
 
-class LocalDOMWindow FINAL : public RefCountedWillBeGarbageCollectedFinalized<LocalDOMWindow>, public EventTargetWithInlineData, public DOMWindowBase64, public FrameDestructionObserver, public WillBeHeapSupplementable<LocalDOMWindow>, public LifecycleContext<LocalDOMWindow> {
+class LocalDOMWindow FINAL : public RefCountedWillBeGarbageCollectedFinalized<LocalDOMWindow>, public EventTargetWithInlineData, public DOMWindowBase64, public DOMWindowPrivateScript, public FrameDestructionObserver, public WillBeHeapSupplementable<LocalDOMWindow>, public LifecycleContext<LocalDOMWindow> {
     DEFINE_WRAPPERTYPEINFO();
     REFCOUNTED_EVENT_TARGET(LocalDOMWindow);
     WILL_BE_USING_GARBAGE_COLLECTED_MIXIN(LocalDOMWindow);