ES6 symbols: Implement Symbol intrinsic and basic functionality

src/arm/lithium-codegen-arm.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 6020 matching lines @@
     __ b(eq, true_label);
     __ cmp(input, Operand(JS_FUNCTION_PROXY_TYPE));
     final_branch_condition = eq;
 
   } else if (type_name->Equals(heap()->object_string())) {
     __ JumpIfSmi(input, false_label);
     if (!FLAG_harmony_typeof) {
       __ CompareRoot(input, Heap::kNullValueRootIndex);
       __ b(eq, true_label);
     }
-    __ CompareObjectType(input, input, scratch,
-                         FIRST_NONCALLABLE_SPEC_OBJECT_TYPE);
+    if (FLAG_harmony_symbols) {
+      __ CompareObjectType(input, input, scratch, SYMBOL_TYPE);
+      __ b(eq, true_label);
+      __ CompareInstanceType(input, scratch,
+                             FIRST_NONCALLABLE_SPEC_OBJECT_TYPE);
+    } else {
+      __ CompareObjectType(input, input, scratch,
+                           FIRST_NONCALLABLE_SPEC_OBJECT_TYPE);
+    }
     __ b(lt, false_label);
     __ CompareInstanceType(input, scratch, LAST_NONCALLABLE_SPEC_OBJECT_TYPE);
     __ b(gt, false_label);
     // Check for undetectable objects => false.
     __ ldrb(ip, FieldMemOperand(input, Map::kBitFieldOffset));
     __ tst(ip, Operand(1 << Map::kIsUndetectable));
     final_branch_condition = eq;
 
   } else {
     __ b(false_label);
@@ skipping 263 matching lines @@
   __ sub(scratch, result, Operand(index, LSL, kPointerSizeLog2 - kSmiTagSize));
   __ ldr(result, FieldMemOperand(scratch,
                                  FixedArray::kHeaderSize - kPointerSize));
   __ bind(&done);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal