Oilpan: fix build after r180052.

R=haraken
BUG=383813

Review URL: https://codereview.chromium.org/463633004

git-svn-id: svn://svn.chromium.org/blink/trunk@180070 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/core/dom/FullscreenElementStack.h

@@ -140,4 +140,13 @@ inline FullscreenElementStack* FullscreenElementStack::fromIfExists(Document& do
 
 } // namespace blink
 
+// Needed by the HeapVector<> element stack.
+namespace WTF {
+
+template<>struct IsPod<blink::FullscreenElementStack::RequestType> {
+    static const bool value = true;
+};
+
+} // namespace WTF
+
 #endif // FullscreenElementStack_h