GC plugin: remove mixin trace override restriction.

tools/clang/blink_gc_plugin/RecordInfo.cpp

 // Copyright 2014 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 "Config.h"
 #include "RecordInfo.h"
 
 using namespace clang;
 using std::string;
 
@@ skipping 347 matching lines @@
          it != record_->method_end(); ++it) {
       if (*it == trace_method_) {
         is_declaring_local_trace_ = kTrue;
         break;
       }
     }
   }
   return is_declaring_local_trace_;
 }
 
-bool RecordInfo::IsGCMixinInstance() {
-  assert(IsGCDerived());
-  if (record_->isAbstract())
-    return false;
-
-  assert(!IsGCMixin());
-
-  // true iff the class derives from GCMixin and
-  // one or more other GC base classes.
-  bool seen_gc_mixin = false;
-  bool seen_gc_derived = false;
-  for (const auto& gc_base : gc_base_names_) {
-    if (Config::IsGCMixinBase(gc_base))
-      seen_gc_mixin = true;
-    else if (Config::IsGCBase(gc_base))
-      seen_gc_derived = true;
-  }
-  return seen_gc_derived && seen_gc_mixin;
-}
-
 // A (non-virtual) class is considered abstract in Blink if it has
 // no public constructors and no create methods.
 bool RecordInfo::IsConsideredAbstract() {
   for (CXXRecordDecl::ctor_iterator it = record_->ctor_begin();
        it != record_->ctor_end();
        ++it) {
     if (!it->isCopyOrMoveConstructor() && it->getAccess() == AS_public)
       return false;
   }
   for (CXXRecordDecl::method_iterator it = record_->method_begin();
@@ skipping 276 matching lines @@
         edge->members().push_back(member);
       }
       // TODO: Handle the case where we fail to create an edge (eg, if the
       // argument is a primitive type or just not fully known yet).
     }
     return edge;
   }
 
   return new Value(info);
 }