ES6 symbols: turn symbols into a proper primitive type

src/code-stubs.cc

Index: src/code-stubs.cc
diff --git a/src/code-stubs.cc b/src/code-stubs.cc
index 95bc1e99cc9f29789f2a36812c8253cff9c150ab..1884b56f11bb32f3959469da4a64ecb2bbb574ee 100644
--- a/src/code-stubs.cc
+++ b/src/code-stubs.cc
@@ -510,6 +510,7 @@ void ToBooleanStub::Types::Print(StringStream* stream) const {
   if (Contains(SMI)) stream->Add("Smi");
   if (Contains(SPEC_OBJECT)) stream->Add("SpecObject");
   if (Contains(STRING)) stream->Add("String");
+  if (Contains(SYMBOL)) stream->Add("Symbol");
   if (Contains(HEAP_NUMBER)) stream->Add("HeapNumber");
 }
 
@@ -549,6 +550,9 @@ bool ToBooleanStub::Types::Record(Handle<Object> object) {
     Add(STRING);
     return !object->IsUndetectableObject() &&
         String::cast(*object)->length() != 0;
+  } else if (object->IsSymbol()) {
+    Add(SYMBOL);
+    return true;
   } else if (object->IsHeapNumber()) {
     ASSERT(!object->IsUndetectableObject());
     Add(HEAP_NUMBER);
@@ -565,6 +569,7 @@ bool ToBooleanStub::Types::Record(Handle<Object> object) {
 bool ToBooleanStub::Types::NeedsMap() const {
   return Contains(ToBooleanStub::SPEC_OBJECT)
       || Contains(ToBooleanStub::STRING)
+      || Contains(ToBooleanStub::SYMBOL)
       || Contains(ToBooleanStub::HEAP_NUMBER);
 }