[es6] Tail calls support.

src/globals.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_GLOBALS_H_
 #define V8_GLOBALS_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 737 matching lines @@
     case ConvertReceiverMode::kNotNullOrUndefined:
       return os << "NOT_NULL_OR_UNDEFINED";
     case ConvertReceiverMode::kAny:
       return os << "ANY";
   }
   UNREACHABLE();
   return os;
 }
 
 
+// Defines whether tail call optimization is allowed.
+enum class TailCallMode : unsigned { kAllow, kDisallow };
+
+inline size_t hash_value(TailCallMode mode) { return bit_cast<unsigned>(mode); }
+
+inline std::ostream& operator<<(std::ostream& os, TailCallMode mode) {
+  switch (mode) {
+    case TailCallMode::kAllow:
+      return os << "ALLOW_TAIL_CALLS";
+    case TailCallMode::kDisallow:
+      return os << "DISALLOW_TAIL_CALLS";
+  }
+  UNREACHABLE();
+  return os;
+}
+
+
 // Used to specify if a macro instruction must perform a smi check on tagged
 // values.
 enum SmiCheckType {
   DONT_DO_SMI_CHECK,
   DO_SMI_CHECK
 };
 
 
 enum ScopeType {
   EVAL_SCOPE,      // The top-level scope for an eval source.
@@ skipping 274 matching lines @@
   kind = static_cast<FunctionKind>(kind | FunctionKind::kInObjectLiteral);
   DCHECK(IsValidFunctionKind(kind));
   return kind;
 }
 }  // namespace internal
 }  // namespace v8
 
 namespace i = v8::internal;
 
 #endif  // V8_GLOBALS_H_