Renamed "symbols" to "internalized strings" throughout the code base,

src/property.h

Index: src/property.h
diff --git a/src/property.h b/src/property.h
index 1cadd57b30dfbe9b40bc93278672502305eb9a2e..3155f44dfff52c60af88b49d5412d21d60d6c8d5 100644
--- a/src/property.h
+++ b/src/property.h
@@ -48,9 +48,9 @@ class Descriptor BASE_EMBEDDED {
     return Smi::cast(value)->value();
   }
 
-  MUST_USE_RESULT MaybeObject* KeyToSymbol() {
-    if (!StringShape(key_).IsSymbol()) {
-      MaybeObject* maybe_result = HEAP->LookupSymbol(key_);
+  MUST_USE_RESULT MaybeObject* KeyToInternalizedString() {
+    if (!StringShape(key_).IsInternalized()) {
+      MaybeObject* maybe_result = HEAP->InternalizeString(key_);
       if (!maybe_result->To(&key_)) return maybe_result;
     }
     return key_;