ES6 symbols: Implement Symbol intrinsic and basic functionality

src/stub-cache.cc

Index: src/stub-cache.cc
diff --git a/src/stub-cache.cc b/src/stub-cache.cc
index c481a74c24fc75538ce10f818bafdd64c02443aa..e8f53a1bfcf57571e3b14ea9f43786828648878b 100644
--- a/src/stub-cache.cc
+++ b/src/stub-cache.cc
@@ -572,6 +572,8 @@ Handle<Code> StubCache::ComputeCallConstant(int argc,
   CheckType check = RECEIVER_MAP_CHECK;
   if (object->IsString()) {
     check = STRING_CHECK;
+  } else if (object->IsSymbol()) {
+    check = SYMBOL_CHECK;
   } else if (object->IsNumber()) {
     check = NUMBER_CHECK;
   } else if (object->IsBoolean()) {
@@ -613,7 +615,8 @@ Handle<Code> StubCache::ComputeCallField(int argc,
   // TODO(1233596): We cannot do receiver map check for non-JS objects
   // because they may be represented as immediates without a
   // map. Instead, we check against the map in the holder.
-  if (object->IsNumber() || object->IsBoolean() || object->IsString()) {
+  if (object->IsNumber() || object->IsSymbol() ||
+      object->IsBoolean() || object->IsString()) {
     object = holder;
   }
 
@@ -651,7 +654,8 @@ Handle<Code> StubCache::ComputeCallInterceptor(int argc,
   // TODO(1233596): We cannot do receiver map check for non-JS objects
   // because they may be represented as immediates without a
   // map. Instead, we check against the map in the holder.
-  if (object->IsNumber() || object->IsBoolean() || object->IsString()) {
+  if (object->IsNumber() || object->IsSymbol() ||
+      object->IsBoolean() || object->IsString()) {
     object = holder;
   }