GC plugin: consider references equal to raw pointers.

tools/clang/blink_gc_plugin/Edge.h

Index: tools/clang/blink_gc_plugin/Edge.h
diff --git a/tools/clang/blink_gc_plugin/Edge.h b/tools/clang/blink_gc_plugin/Edge.h
index 2ea8e544e8e6905ada5f967321683fde0ed8a89a..29e5f25b1d1253f884bfce0bce5f92f3635d5ff5 100644
--- a/tools/clang/blink_gc_plugin/Edge.h
+++ b/tools/clang/blink_gc_plugin/Edge.h
@@ -124,8 +124,14 @@ class PtrEdge : public Edge {
 
 class RawPtr : public PtrEdge {
  public:
-  explicit RawPtr(Edge* ptr, bool is_ptr_class)
-      : PtrEdge(ptr), is_ptr_class_(is_ptr_class) { }
+  RawPtr(Edge* ptr, bool is_ptr_class, bool is_ref_type)
+      : PtrEdge(ptr)
+      , is_ptr_class_(is_ptr_class)
+      , is_ref_type_(is_ref_type)
+  {
+      assert(!(is_ptr_class_ && is_ref_type_));
+  }
+
   bool IsRawPtr() { return true; }
   bool IsRawPtrClass() { return is_ptr_class_; }
   LivenessKind Kind() { return kWeak; }
@@ -134,8 +140,11 @@ class RawPtr : public PtrEdge {
     return TracingStatus::Unneeded();
   }
   void Accept(EdgeVisitor* visitor) { visitor->VisitRawPtr(this); }
+
+  bool HasReferenceType() { return is_ref_type_; }
  private:
   bool is_ptr_class_;
+  bool is_ref_type_;
 };
 
 class RefPtr : public PtrEdge {