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

tools/clang/blink_gc_plugin/CheckFieldsVisitor.cpp

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "CheckFieldsVisitor.h"
 
 #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_;
 }
 
 bool CheckFieldsVisitor::ContainsInvalidFields(RecordInfo* info) {
   stack_allocated_host_ = info->IsStackAllocated();
   managed_host_ = stack_allocated_host_ ||
                   info->IsGCAllocated() ||
                   info->IsNonNewable() ||
                   info->IsOnlyPlacementNewable();
   for (RecordInfo::Fields::iterator it = info->GetFields().begin();
        it != info->GetFields().end();
        ++it) {
     context().clear();
     current_ = &it->second;
     current_->edge()->Accept(this);
   }
   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.
   for (Context::iterator it = context().begin();
        it != context().end();
        ++it) {
     if ((*it)->Kind() == Edge::kRoot)
       return;
   }
   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;
 
   if (edge->IsUnsafe())
     invalid_fields_.push_back(std::make_pair(current_, kIteratorToGCManaged));
 }
 
 void CheckFieldsVisitor::AtValue(Value* edge) {
   // TODO: what should we do to check unions?
@@ skipping 64 matching lines @@
       return kRawPtrToGCManaged;
   }
   if (ptr->IsRefPtr())
     return kRefPtrToGCManaged;
   if (ptr->IsOwnPtr())
     return kOwnPtrToGCManaged;
   if (ptr->IsUniquePtr())
     return kUniquePtrToGCManaged;
   assert(false && "Unknown smart pointer kind");
 }