blink_gc_plugin should require tracing for classes that have a trace method

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"
 #include "clang/Sema/Sema.h"
 
 using namespace clang;
 using std::string;
@@ skipping 269 matching lines @@
   if (IsStackAllocated())
     return false;
   unsigned bases_with_trace = 0;
   for (Bases::iterator it = GetBases().begin(); it != GetBases().end(); ++it) {
     if (it->second.NeedsTracing().IsNeeded())
       ++bases_with_trace;
   }
   if (bases_with_trace > 1)
     return true;
   GetFields();
-  return fields_need_tracing_.IsNeeded();
+  return fields_need_tracing_.IsNeeded() || GetTraceMethod();
 }
 
 // Get the actual tracing method (ie, can be traceAfterDispatch if there is a
 // dispatch method).
 CXXMethodDecl* RecordInfo::GetTraceMethod() {
   DetermineTracingMethods();
   return trace_method_;
 }
 
 // Get the static trace dispatch method.
@@ skipping 354 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);
 }