[es6] Initial steps towards a correct implementation of IsCallable.

src/execution.h

 // Copyright 2014 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_EXECUTION_H_
 #define V8_EXECUTION_H_
 
 #include "src/allocation.h"
 #include "src/base/atomicops.h"
 #include "src/handles.h"
@@ skipping 74 matching lines @@
       Isolate* isolate, Handle<Object> obj);
 
   // Create a new date object from 'time'.
   MUST_USE_RESULT static MaybeHandle<Object> NewDate(
       Isolate* isolate, double time);
 
   // Create a new regular expression object from 'pattern' and 'flags'.
   MUST_USE_RESULT static MaybeHandle<JSRegExp> NewJSRegExp(
       Handle<String> pattern, Handle<String> flags);
 
-  static Handle<Object> GetFunctionFor();
   static Handle<String> GetStackTraceLine(Handle<Object> recv,
                                           Handle<JSFunction> fun,
                                           Handle<Object> pos,
                                           Handle<Object> is_global);
 
-  // Get a function delegate (or undefined) for the given non-function
-  // object. Used for support calling objects as functions.
-  static Handle<Object> GetFunctionDelegate(Isolate* isolate,
-                                            Handle<Object> object);
-  MUST_USE_RESULT static MaybeHandle<Object> TryGetFunctionDelegate(
-      Isolate* isolate,
-      Handle<Object> object);
+  // Get a function delegate for the given non-function object.
+  // Used for support calling objects as functions.
+  MUST_USE_RESULT static MaybeHandle<JSFunction> GetFunctionDelegate(
+      Isolate* isolate, Handle<Object> object);
 
   // Get a function delegate (or undefined) for the given non-function
   // object. Used for support calling objects as constructors.
-  static Handle<Object> GetConstructorDelegate(Isolate* isolate,
-                                               Handle<Object> object);
-  static MaybeHandle<Object> TryGetConstructorDelegate(Isolate* isolate,
+  MUST_USE_RESULT static MaybeHandle<JSFunction> GetConstructorDelegate(
+      Isolate* isolate, Handle<Object> object);
+
+ private:
+  MUST_USE_RESULT static Handle<String> RenderCallSite(Isolate* isolate,
                                                        Handle<Object> object);
 };
 
 
 class ExecutionAccess;
 class PostponeInterruptsScope;
 
 
 // StackGuard contains the handling of the limits that are used to limit the
 // number of nested invocations of JavaScript and the stack size used in each
@@ skipping 159 matching lines @@
   friend class Isolate;
   friend class StackLimitCheck;
   friend class PostponeInterruptsScope;
 
   DISALLOW_COPY_AND_ASSIGN(StackGuard);
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_EXECUTION_H_