Upgrade Symbol implementation to match current ES6 behavior.

src/ia32/code-stubs-ia32.cc

Index: src/ia32/code-stubs-ia32.cc
diff --git a/src/ia32/code-stubs-ia32.cc b/src/ia32/code-stubs-ia32.cc
index e280c50e7937d30eb3344017332ee6156a5b33bb..fc32866c68c35a46c20d6ac59fbaa34657bca64e 100644
--- a/src/ia32/code-stubs-ia32.cc
+++ b/src/ia32/code-stubs-ia32.cc
@@ -2433,7 +2433,16 @@ void CallFunctionStub::Generate(MacroAssembler* masm) {
 
   if (CallAsMethod()) {
     if (NeedsChecks()) {
-      // Do not transform the receiver for strict mode functions.
+     // FIXME: expedient but expensive; surely a better way?
+      // Always call ToObject() on symbol values.
+      Label not_a_symbol;
+      __ mov(eax, Operand(esp, (argc_ + 1) * kPointerSize));
+      __ JumpIfSmi(eax, &not_a_symbol, Label::kNear);
+      __ CmpObjectType(eax, SYMBOL_TYPE, ecx);
+      __ j(equal, &wrap);
+
+      __ bind(&not_a_symbol);
+       // Do not transform the receiver for strict mode functions.
       __ mov(ecx, FieldOperand(edi, JSFunction::kSharedFunctionInfoOffset));
       __ test_b(FieldOperand(ecx, SharedFunctionInfo::kStrictModeByteOffset),
                 1 << SharedFunctionInfo::kStrictModeBitWithinByte);