[oilpan] Resurrect a loop-back persistent handle in RefCountedHeapAllocated

Source/wtf/SizeLimits.cpp

Index: Source/wtf/SizeLimits.cpp
diff --git a/Source/wtf/SizeLimits.cpp b/Source/wtf/SizeLimits.cpp
index 60c180eb18a5aa5994861187e450a10745204bbc..b5e02c6992742b72a66d6fce067b9c296dfdf87e 100644
--- a/Source/wtf/SizeLimits.cpp
+++ b/Source/wtf/SizeLimits.cpp
@@ -43,9 +43,11 @@ namespace WTF {
 #ifndef NDEBUG
 struct SameSizeAsRefCounted {
     int a;
-    bool b;
-    bool c;
-    ThreadRestrictionVerifier d;
+    // FIXME(oilpan): Remove the following comment-outs once we replace
+    // all RefCountedHeapAllocated with HeapAllocated.
+    // bool b;
+    // bool c;
+    // ThreadRestrictionVerifier d;
     // The debug version may get bigger.
 };
 #else