GC plugin: improve error reporting when tracing illegal fields.

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 e5d69f0b897c0a13e8b0b0cbdc2b544632b38272..396ed95bf1cfea3de07cc57799a899c8e2678101 100644
--- a/tools/clang/blink_gc_plugin/CheckFieldsVisitor.cpp
+++ b/tools/clang/blink_gc_plugin/CheckFieldsVisitor.cpp
@@ -86,6 +86,7 @@ void CheckFieldsVisitor::AtValue(Value* edge) {
 
   // Disallow  OwnPtr<T>, RefPtr<T> and T* to stack-allocated types.
   if (Parent()->IsOwnPtr() ||
+      Parent()->IsUniquePtr() ||
       Parent()->IsRefPtr() ||
       (stack_allocated_host_ && Parent()->IsRawPtr())) {
     invalid_fields_.push_back(std::make_pair(
@@ -103,6 +104,8 @@ void CheckFieldsVisitor::AtValue(Value* edge) {
 void CheckFieldsVisitor::AtCollection(Collection* edge) {
   if (edge->on_heap() && Parent() && Parent()->IsOwnPtr())
     invalid_fields_.push_back(std::make_pair(current_, kOwnPtrToGCManaged));
+  if (edge->on_heap() && Parent() && Parent()->IsUniquePtr())
+    invalid_fields_.push_back(std::make_pair(current_, kUniquePtrToGCManaged));
 }
 
 CheckFieldsVisitor::Error CheckFieldsVisitor::InvalidSmartPtr(Edge* ptr) {
@@ -116,5 +119,7 @@ CheckFieldsVisitor::Error CheckFieldsVisitor::InvalidSmartPtr(Edge* ptr) {
     return kRefPtrToGCManaged;
   if (ptr->IsOwnPtr())
     return kOwnPtrToGCManaged;
+  if (ptr->IsUniquePtr())
+    return kUniquePtrToGCManaged;
   assert(false && "Unknown smart pointer kind");
 }