[BlinkGCPlugin] Allow tracing member in traceImpl.

tools/clang/blink_gc_plugin/BlinkGCPlugin.cpp

Index: tools/clang/blink_gc_plugin/BlinkGCPlugin.cpp
diff --git a/tools/clang/blink_gc_plugin/BlinkGCPlugin.cpp b/tools/clang/blink_gc_plugin/BlinkGCPlugin.cpp
index d24d67ade4ff4c37aa2016b8d4d76567ea422652..1e407c9df482ddddb7d08d075ac4d3a43189dede 100644
--- a/tools/clang/blink_gc_plugin/BlinkGCPlugin.cpp
+++ b/tools/clang/blink_gc_plugin/BlinkGCPlugin.cpp
@@ -322,7 +322,9 @@ class CheckDispatchVisitor : public RecursiveASTVisitor<CheckDispatchVisitor> {
 class CheckTraceVisitor : public RecursiveASTVisitor<CheckTraceVisitor> {
  public:
   CheckTraceVisitor(CXXMethodDecl* trace, RecordInfo* info)
-      : trace_(trace), info_(info) {}
+      : trace_(trace), info_(info), delegates_to_traceimpl_(false) {}
+
+  bool delegates_to_traceimpl() const { return delegates_to_traceimpl_; }
 
   bool VisitMemberExpr(MemberExpr* member) {
     // In weak callbacks, consider any occurrence as a correct usage.
@@ -383,6 +385,11 @@ class CheckTraceVisitor : public RecursiveASTVisitor<CheckTraceVisitor> {
     if (CXXMemberCallExpr* expr = dyn_cast<CXXMemberCallExpr>(call)) {
       if (CheckTraceFieldCall(expr) || CheckRegisterWeakMembers(expr))
         return true;
+
+      if (expr->getMethodDecl()->getNameAsString() == kTraceImplName) {
+        delegates_to_traceimpl_ = true;
+        return true;
+      }
     }
 
     CheckTraceBaseCall(call);
@@ -415,6 +422,23 @@ class CheckTraceVisitor : public RecursiveASTVisitor<CheckTraceVisitor> {
   void CheckCXXDependentScopeMemberExpr(CallExpr* call,
                                         CXXDependentScopeMemberExpr* expr) {
     string fn_name = expr->getMember().getAsString();
+
+    // Check for VisitorDispatcher::trace(field)
+    if (!expr->isImplicitAccess()) {
+      if (clang::DeclRefExpr* base_decl =
+              clang::dyn_cast<clang::DeclRefExpr>(expr->getBase())) {
+        if (Config::IsVisitorDispatcherType(base_decl->getType()) &&
+            call->getNumArgs() == 1 && fn_name == kTraceName) {
+          FindFieldVisitor finder;
+          finder.TraverseStmt(call->getArg(0));
+          if (finder.field())
+            FoundField(finder.field());
+
+          return;
+        }
+      }
+    }
+
     CXXRecordDecl* tmpl = GetDependentTemplatedDecl(expr);
     if (!tmpl)
       return;
@@ -565,6 +589,7 @@ class CheckTraceVisitor : public RecursiveASTVisitor<CheckTraceVisitor> {
 
   CXXMethodDecl* trace_;
   RecordInfo* info_;
+  bool delegates_to_traceimpl_;
 };
 
 // This visitor checks that the fields of a class and the fields of
@@ -1303,6 +1328,11 @@ class BlinkGCPluginConsumer : public ASTConsumer {
     CheckTraceVisitor visitor(trace, parent);
     visitor.TraverseCXXMethodDecl(trace);
 
+    // Skip reporting if this trace method is a just delegate to
+    // traceImpl method. We will report on CheckTraceMethod on traceImpl method.
+    if (visitor.delegates_to_traceimpl())
+      return;
+
     for (RecordInfo::Bases::iterator it = parent->GetBases().begin();
          it != parent->GetBases().end();
          ++it) {