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

tools/clang/blink_gc_plugin/CheckFieldsVisitor.cpp

Index: tools/clang/blink_gc_plugin/CheckFieldsVisitor.cpp
diff --git a/tools/clang/blink_gc_plugin/CheckFieldsVisitor.cpp b/tools/clang/blink_gc_plugin/CheckFieldsVisitor.cpp
index 05419da6d67eb71958ecd944bf247bfe3803fee9..735ec0e8858a4d45da5feda4799da14b63d3e889 100644
--- a/tools/clang/blink_gc_plugin/CheckFieldsVisitor.cpp
+++ b/tools/clang/blink_gc_plugin/CheckFieldsVisitor.cpp
@@ -6,13 +6,10 @@
 
 #include <cassert>
 
-#include "BlinkGCPluginOptions.h"
 #include "RecordInfo.h"
 
-CheckFieldsVisitor::CheckFieldsVisitor()
-    : current_(0),
-      stack_allocated_host_(false) {
-}
+CheckFieldsVisitor::CheckFieldsVisitor(const BlinkGCPluginOptions& options)
+    : options_(options), current_(0), stack_allocated_host_(false) {}
 
 CheckFieldsVisitor::Errors& CheckFieldsVisitor::invalid_fields() {
   return invalid_fields_;
@@ -34,7 +31,7 @@ bool CheckFieldsVisitor::ContainsInvalidFields(RecordInfo* info) {
   return !invalid_fields_.empty();
 }
 
-void CheckFieldsVisitor::AtMember(Member* edge) {
+void CheckFieldsVisitor::AtMember(Member*) {
   if (managed_host_)
     return;
   // A member is allowed to appear in the context of a root.
@@ -47,6 +44,14 @@ void CheckFieldsVisitor::AtMember(Member* edge) {
   invalid_fields_.push_back(std::make_pair(current_, kMemberInUnmanaged));
 }
 
+void CheckFieldsVisitor::AtWeakMember(WeakMember*) {
+  // TODO(sof): remove this once crbug.com/724418's change
+  // has safely been rolled out.
+  if (options_.enable_weak_members_in_unmanaged_classes)
+    return;
+  AtMember(nullptr);
+}
+
 void CheckFieldsVisitor::AtIterator(Iterator* edge) {
   if (!managed_host_)
     return;