Oilpan: exempt CSSBasicShapeValue from GC plugin checking.

third_party/WebKit/Source/core/css/CSSBasicShapeValue.h

Index: third_party/WebKit/Source/core/css/CSSBasicShapeValue.h
diff --git a/third_party/WebKit/Source/core/css/CSSBasicShapeValue.h b/third_party/WebKit/Source/core/css/CSSBasicShapeValue.h
index 1a48965b7f7e997257efaa2da7025ab9e9bd34e2..2b5397b36974ea4eeb1ebe722a1c8506ebc899d2 100644
--- a/third_party/WebKit/Source/core/css/CSSBasicShapeValue.h
+++ b/third_party/WebKit/Source/core/css/CSSBasicShapeValue.h
@@ -40,7 +40,10 @@
 
 namespace blink {
 
-class CORE_EXPORT CSSBasicShapeValue : public CSSValue {
+// TODO(Oilpan): the GC plugin is not capable of understanding that
+// the traceAfterDispatch() method covers subtypes of CSSBasicShapeValue.
+// Temporarily exempt it from being checked
+class CORE_EXPORT GC_PLUGIN_IGNORE("535448") CSSBasicShapeValue : public CSSValue {
 public:
     enum Type {
         CSSBasicShapeEllipseType,