Have ScriptPromiseResolver on the Oilpan heap always.

Source/modules/imagebitmap/WindowImageBitmapFactories.cpp

Index: Source/modules/imagebitmap/WindowImageBitmapFactories.cpp
diff --git a/Source/modules/imagebitmap/WindowImageBitmapFactories.cpp b/Source/modules/imagebitmap/WindowImageBitmapFactories.cpp
index 841fa2309c54f0b170e7af4305877c22215d6498..2d02ab5c44381840a71e2e00d80e144cb0477180 100644
--- a/Source/modules/imagebitmap/WindowImageBitmapFactories.cpp
+++ b/Source/modules/imagebitmap/WindowImageBitmapFactories.cpp
@@ -68,7 +68,7 @@ static IntSize sizeFor(HTMLVideoElement* video)
 
 static ScriptPromise fulfillImageBitmap(ScriptState* scriptState, PassRefPtrWillBeRawPtr<ImageBitmap> imageBitmap)
 {
-    RefPtrWillBeRawPtr<ScriptPromiseResolver> resolver = ScriptPromiseResolver::create(scriptState);
+    ScriptPromiseResolver* resolver = ScriptPromiseResolver::create(scriptState);
     ScriptPromise promise = resolver->promise();
     if (imageBitmap) {
         resolver->resolve(imageBitmap);