Speed up compares with characters ie single-character strings....

src/objects-inl.h

Index: src/objects-inl.h
===================================================================
--- src/objects-inl.h	(revision 3561)
+++ src/objects-inl.h	(working copy)
@@ -150,8 +150,12 @@
 bool Object::IsSymbol() {
   if (!this->IsHeapObject()) return false;
   uint32_t type = HeapObject::cast(this)->map()->instance_type();
-  return (type & (kIsNotStringMask | kIsSymbolMask)) ==
-         (kStringTag | kSymbolTag);
+  // Because the symbol tag is non-zero and no non-string types have the
+  // symbol bit set we can test for symbols with a very simple test
+  // operation.
+  ASSERT(kSymbolTag != 0);
+  ASSERT(kNotStringTag + kIsSymbolMask > LAST_TYPE);
+  return (type & kIsSymbolMask != 0);
 }
 
 
@@ -226,7 +230,8 @@
 
 bool StringShape::IsSymbol() {
   ASSERT(valid());
-  return (type_ & kIsSymbolMask) == kSymbolTag;
+  ASSERT(kSymbolTag != 0);
+  return (type_ & kIsSymbolMask) != 0;
 }