Blink GC plugin: require a trace method if a class derives multiple bases that need tracing.

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 222 matching lines @@
 CXXMethodDecl* RecordInfo::DeclaresNewOperator() {
   for (CXXRecordDecl::method_iterator it = record_->method_begin();
        it != record_->method_end();
        ++it) {
     if (it->getNameAsString() == kNewOperatorName && it->getNumParams() == 1)
       return *it;
   }
   return 0;
 }
 
-// An object requires a tracing method if it has any fields that need tracing.
+// An object requires a tracing method if it has any fields that need tracing
+// or if it inherits from multiple bases that need tracing.
 bool RecordInfo::RequiresTraceMethod() {
   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();
 }
 
 // Get the actual tracing method (ie, can be traceAfterDispatch if there is a
 // dispatch method).
 CXXMethodDecl* RecordInfo::GetTraceMethod() {
   DetermineTracingMethods();
   return trace_method_;
 }
@@ skipping 259 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);
 }