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

Source/core/frame/DOMWindowPrivateScript.h

Index: Source/core/frame/DOMWindowPrivateScript.h
diff --git a/Source/platform/PlatformResourceLoader.h b/Source/core/frame/DOMWindowPrivateScript.h
similarity index 53%
copy from Source/platform/PlatformResourceLoader.h
copy to Source/core/frame/DOMWindowPrivateScript.h
index e2db013c6374320729c668ddc9cee5f5f198294f..889598c0f1d159803be707610d2239b122ce3a54 100644
--- a/Source/platform/PlatformResourceLoader.h
+++ b/Source/core/frame/DOMWindowPrivateScript.h
@@ -2,16 +2,18 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef PlatformResourceLoader_h
-#define PlatformResourceLoader_h
+#ifndef DOMWindowPrivateScript_h
+#define DOMWindowPrivateScript_h
 
-#include "platform/PlatformExport.h"
 #include "wtf/text/WTFString.h"
 
 namespace blink {
 
-PLATFORM_EXPORT String loadResourceAsASCIIString(const char* resource);
+class DOMWindowPrivateScript {
+public:
+    String loadPlatformResource(const String& name);
+};
 
 } // namespace blink
 
-#endif // PlatformResourceLoader_h
+#endif // DOMWindowPrivateScript_h