[es6] Bound function names

https://people.mozilla.org/~jorendorff/es6-draft.html#sec-function.prototype.bind

Bound functions should have a name based on the function that was
bound.

BUG=N
LOG=N
R=adamk   CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:linux_chromium_rel_ng;tryserver.blink:linux_blink_rel

Review URL: https://codereview.chromium.org/1182513002

Cr-Commit-Position: refs/heads/master@{#28968}

src/v8natives.js

@@ -21,6 +21,7 @@ var GlobalFunction = global.Function;
 var GlobalNumber = global.Number;
 var GlobalObject = global.Object;
 var InternalArray = utils.InternalArray;
+var SetFunctionName = utils.SetFunctionName;
 
 var MathAbs;
 var ProxyDelegateCallAndConstruct;
@@ -1764,6 +1765,10 @@ function FunctionBind(this_arg) { // Length is 1.
   var result = %FunctionBindArguments(boundFunction, this,
                                       this_arg, new_length);
 
+  var name = this.name;
+  var bound_name = IS_STRING(name) ? name : "";
+  SetFunctionName(result, bound_name, "bound");
+
   // We already have caller and arguments properties on functions,
   // which are non-configurable. It therefore makes no sence to
   // try to redefine these as defined by the spec. The spec says

test/mjsunit/function-bind-name.js

+// Copyright 2015 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.
+
+function f() {}
+var fb = f.bind({});
+assertEquals('bound f', fb.name);
+assertEquals('function bound f() { [native code] }', fb.toString());
+
+Object.defineProperty(f, 'name', {value: 42});
+var fb2 = f.bind({});
+assertEquals('bound ', fb2.name);
+assertEquals('function bound () { [native code] }', fb2.toString());