Correctly visit all external strings.

src/heap.cc

Index: src/heap.cc
diff --git a/src/heap.cc b/src/heap.cc
index 11bf9cd4d4a92909bc0d7b9cbc4260cf8622aaeb..468a01d6949bc2cdf20928dcb4eb33da3af36400 100644
--- a/src/heap.cc
+++ b/src/heap.cc
@@ -1576,13 +1576,40 @@ void Heap::ProcessWeakReferences(WeakObjectRetainer* retainer) {
 void Heap::VisitExternalResources(v8::ExternalResourceVisitor* visitor) {
   AssertNoAllocation no_allocation;
 
-  class VisitorAdapter : public ObjectVisitor {
+  // Both the external string table and the symbol table may contain
+  // external strings, but neither lists them exhaustively, nor is the
+  // intersection set empty.  Therefore we iterate over the external string
+  // table first, ignoring symbols, and then over the symbol table.
+
+  class ExternalStringTableVisitorAdapter : public ObjectVisitor {
+   public:
+    explicit ExternalStringTableVisitorAdapter(
+        v8::ExternalResourceVisitor* visitor) : visitor_(visitor) {}
+    virtual void VisitPointers(Object** start, Object** end) {
+      for (Object** p = start; p < end; p++) {
+        // Visit non-symbol external strings,
+        // since symbols are listed in the symbol table.
+        if (!(*p)->IsSymbol()) {
+          ASSERT((*p)->IsExternalString());
+          visitor_->VisitExternalString(Utils::ToLocal(
+              Handle<String>(String::cast(*p))));
+        }
+      }
+    }
+   private:
+    v8::ExternalResourceVisitor* visitor_;
+  } external_string_table_visitor(visitor);
+
+  external_string_table_.Iterate(&external_string_table_visitor);
+
+  class SymbolTableVisitorAdapter : public ObjectVisitor {
    public:
-    explicit VisitorAdapter(v8::ExternalResourceVisitor* visitor)
-        : visitor_(visitor) {}
+    explicit SymbolTableVisitorAdapter(
+        v8::ExternalResourceVisitor* visitor) : visitor_(visitor) {}
     virtual void VisitPointers(Object** start, Object** end) {
       for (Object** p = start; p < end; p++) {
         if ((*p)->IsExternalString()) {
+          ASSERT((*p)->IsSymbol());
           visitor_->VisitExternalString(Utils::ToLocal(
               Handle<String>(String::cast(*p))));
         }
@@ -1590,8 +1617,9 @@ void Heap::VisitExternalResources(v8::ExternalResourceVisitor* visitor) {
     }
    private:
     v8::ExternalResourceVisitor* visitor_;
-  } visitor_adapter(visitor);
-  external_string_table_.Iterate(&visitor_adapter);
+  } symbol_table_visitor(visitor);
+
+  symbol_table()->IterateElements(&symbol_table_visitor);
 }