Oilpan: use Member<> for FilterEffect's filter reference.

Source/platform/graphics/filters/FilterEffect.h

Index: Source/platform/graphics/filters/FilterEffect.h
diff --git a/Source/platform/graphics/filters/FilterEffect.h b/Source/platform/graphics/filters/FilterEffect.h
index e23f939dc99161cd49cbfee8e56d822f99c771b6..7739ab3b40846d34a0791fd52f23dab20b9b27b8 100644
--- a/Source/platform/graphics/filters/FilterEffect.h
+++ b/Source/platform/graphics/filters/FilterEffect.h
@@ -178,7 +178,7 @@ private:
     // The maximum size of a filter primitive. In SVG this is the primitive subregion in absolute coordinate space.
     // The absolute paint rect should never be bigger than m_maxEffectRect.
     FloatRect m_maxEffectRect;
-    Filter* m_filter;
+    RawPtrWillBeMember<Filter> m_filter;
 
     // The following member variables are SVG specific and will move to RenderSVGResourceFilterPrimitive.
     // See bug https://bugs.webkit.org/show_bug.cgi?id=45614.