src: make Symbol more resilient

Instead of crashing if llnode fails to parse a Symbol, just return  a
??? token.

PR-URL: #330
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>

src/llv8-constants.cc

@@ -550,7 +550,7 @@ void Frame::Load() {
 
 
 void Symbol::Load() {
-  kNameOffset = LoadConstant("class_Symbol__name__Object");
+  kNameOffset = LoadConstant({"class_Symbol__name__Object"});
 }
 
 

src/llv8-constants.h

@@ -509,7 +509,7 @@ class Symbol : public Module {
  public:
   CONSTANTS_DEFAULT_METHODS(Symbol);
 
-  int64_t kNameOffset;
+  Constant<int64_t> kNameOffset;
 
  protected:
   void Load();

src/llv8-inl.h

@@ -281,7 +281,7 @@ ACCESSOR(Map, MaybeConstructor, map()->kMaybeConstructorOffset, HeapObject)
 SAFE_ACCESSOR(Map, InstanceDescriptors, map()->kInstanceDescriptorsOffset,
               HeapObject)
 
-ACCESSOR(Symbol, Name, symbol()->kNameOffset, HeapObject)
+SAFE_ACCESSOR(Symbol, Name, symbol()->kNameOffset, HeapObject)
 
 inline int64_t Map::BitField3(Error& err) {
   return v8()->LoadUnsigned(LeaField(v8()->map()->kBitField3Offset), 4, err);

src/llv8.cc

@@ -729,6 +729,7 @@ std::string Symbol::ToString(Error& err) {
     return "Symbol()";
   }
   HeapObject name = Name(err);
+  RETURN_IF_INVALID(name, "Symbol(???)");
   return "Symbol('" + String(name).ToString(err) + "')";
 }