blink_gc_plugin: disallow WeakMember<> fields in off-heap objects.

tools/clang/blink_gc_plugin/CheckFieldsVisitor.h

Index: tools/clang/blink_gc_plugin/CheckFieldsVisitor.h
diff --git a/tools/clang/blink_gc_plugin/CheckFieldsVisitor.h b/tools/clang/blink_gc_plugin/CheckFieldsVisitor.h
index c6ddd5edba1f239d989e39ff6f78f3d02d212251..c47f1d41072f598911817fd6015b49c25efb736e 100644
--- a/tools/clang/blink_gc_plugin/CheckFieldsVisitor.h
+++ b/tools/clang/blink_gc_plugin/CheckFieldsVisitor.h
@@ -7,6 +7,7 @@
 
 #include <vector>
 
+#include "BlinkGCPluginOptions.h"
 #include "Edge.h"
 
 class FieldPoint;
@@ -34,20 +35,23 @@ class CheckFieldsVisitor : public RecursiveEdgeVisitor {
 
   using Errors = std::vector<std::pair<FieldPoint*, Error>>;
 
-  CheckFieldsVisitor();
+  explicit CheckFieldsVisitor(const BlinkGCPluginOptions&);
 
   Errors& invalid_fields();
 
   bool ContainsInvalidFields(RecordInfo* info);
 
-  void AtMember(Member* edge) override;
-  void AtValue(Value* edge) override;
-  void AtCollection(Collection* edge) override;
+  void AtMember(Member*) override;
+  void AtWeakMember(WeakMember*) override;
+  void AtValue(Value*) override;
+  void AtCollection(Collection*) override;
   void AtIterator(Iterator*) override;
 
  private:
   Error InvalidSmartPtr(Edge* ptr);
 
+  const BlinkGCPluginOptions& options_;
+
   FieldPoint* current_;
   bool stack_allocated_host_;
   bool managed_host_;