Oilpan: fix build after r198788.

Source/core/inspector/InspectorDebuggerAgent.cpp

Index: Source/core/inspector/InspectorDebuggerAgent.cpp
diff --git a/Source/core/inspector/InspectorDebuggerAgent.cpp b/Source/core/inspector/InspectorDebuggerAgent.cpp
index 28d6f642f88ca715f8e43260612602e735be752b..142d4c13319774dea924daa794c0dee33ab37270 100644
--- a/Source/core/inspector/InspectorDebuggerAgent.cpp
+++ b/Source/core/inspector/InspectorDebuggerAgent.cpp
@@ -899,7 +899,7 @@ bool InspectorDebuggerAgent::callStackForId(ErrorString* errorString, const Stri
         *errorString = "Async call stack not found";
         return false;
     }
-    RefPtr<AsyncCallStack> asyncStack = m_currentAsyncCallChain->callStacks()[asyncOrdinal - 1];
+    RefPtrWillBeRawPtr<AsyncCallStack> asyncStack = m_currentAsyncCallChain->callStacks()[asyncOrdinal - 1];
     *callStack = asyncStack->callFrames();
     *isAsync = true;
     return true;