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

Source/platform/graphics/filters/SkiaImageFilterBuilder.cpp

Index: Source/platform/graphics/filters/SkiaImageFilterBuilder.cpp
diff --git a/Source/platform/graphics/filters/SkiaImageFilterBuilder.cpp b/Source/platform/graphics/filters/SkiaImageFilterBuilder.cpp
index 8fb67d580a8aa1f78947a56d6b3155319d24c259..40bebe2ae677fe57305a11b5d87c68dfd5cdc43d 100644
--- a/Source/platform/graphics/filters/SkiaImageFilterBuilder.cpp
+++ b/Source/platform/graphics/filters/SkiaImageFilterBuilder.cpp
@@ -41,14 +41,14 @@
 namespace blink {
 
 SkiaImageFilterBuilder::SkiaImageFilterBuilder()
-    : m_context(0)
-    , m_sourceGraphic(0)
+    : m_context(nullptr)
+    , m_sourceGraphic(nullptr)
 {
 }
 
 SkiaImageFilterBuilder::SkiaImageFilterBuilder(GraphicsContext* context)
     : m_context(context)
-    , m_sourceGraphic(0)
+    , m_sourceGraphic(nullptr)
 {
 }