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

Source/core/html/shadow/PluginPlaceholderElement.cpp

Index: Source/core/html/shadow/PluginPlaceholderElement.cpp
diff --git a/Source/core/html/shadow/PluginPlaceholderElement.cpp b/Source/core/html/shadow/PluginPlaceholderElement.cpp
index cf0116602c78cc02d4d9d0b9ffb6f3fbf137c576..cfbc9d5832672e0bafd2067de4c1572c3c4f29a0 100644
--- a/Source/core/html/shadow/PluginPlaceholderElement.cpp
+++ b/Source/core/html/shadow/PluginPlaceholderElement.cpp
@@ -7,7 +7,10 @@
 
 #include "bindings/core/v8/V8PluginPlaceholderElement.h"
 #include "core/dom/Document.h"
+#include "core/html/HTMLStyleElement.h"
+#include "public/platform/Platform.h"
 #include "wtf/Assertions.h"
+#include "wtf/text/WTFString.h"
 
 namespace blink {
 
@@ -31,4 +34,15 @@ void PluginPlaceholderElement::setMessage(const String& htmlMessage)
     ASSERT_UNUSED(success, success);
 }
 
+PassRefPtrWillBeRawPtr<HTMLStyleElement> PluginPlaceholderElement::createStyleElement()
+{
+    const WebData& styleData = Platform::current()->loadResource("PluginPlaceholderElement.css");
+    ASSERT(!styleData.isEmpty());
+    String styleSource(styleData.data(), styleData.size());
+    RefPtrWillBeRawPtr<HTMLStyleElement> styleElement = HTMLStyleElement::create(document(), false);
+    styleElement->setTextContent(styleSource);
+    styleElement->whitelistSource(styleSource);
+    return styleElement.release();
+}
+
 } // namespace blink