Revert of 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 396ed95bf1cfea3de07cc57799a899c8e2678101..e5d69f0b897c0a13e8b0b0cbdc2b544632b38272 100644
--- a/tools/clang/blink_gc_plugin/CheckFieldsVisitor.cpp
+++ b/tools/clang/blink_gc_plugin/CheckFieldsVisitor.cpp
@@ -86,7 +86,6 @@
 
   // 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(
@@ -104,8 +103,6 @@
 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) {
@@ -119,7 +116,5 @@
     return kRefPtrToGCManaged;
   if (ptr->IsOwnPtr())
     return kOwnPtrToGCManaged;
-  if (ptr->IsUniquePtr())
-    return kUniquePtrToGCManaged;
   assert(false && "Unknown smart pointer kind");
 }