Fix V8 callback binding for "CallWith=ThisValue" attribute.

LayoutTests/http/tests/serviceworker/resources/headermap-worker.js

 importScripts('worker-test-helpers.js');
 
 test(function() {
     var expectedMap = {
         'Content-Language': 'ja',
         'Content-Type': 'text/html; charset=UTF-8',
         'X-ServiceWorker-Test': 'response test field'
     };
 
     var headers = new HeaderMap;
@@ skipping 64 matching lines @@
         expectedMap[key] = expectedValue;
     });
 
     // 'forEach()'
     headers.forEach(function(value, key) {
         assert_true(key != deleteKey);
         assert_true(key in expectedMap);
         assert_equals(headers.get(key), expectedMap[key]);
     });
 
+    // 'forEach()' with thisArg
+    var that = {}, saw_that;
+    headers = new HeaderMap;
+    headers.set('a', 'b');
+    headers.forEach(function() { saw_that = this; }, that);
+    assert_equals(saw_that, that, 'Passed thisArg should match');
+
+    headers.forEach(function() { 'use strict'; saw_that = this; }, 'abc');
+    assert_equals(saw_that, 'abc', 'Passed non-object thisArg should match');
+
+    headers.forEach(function() { saw_that = this; }, null);
+    assert_equals(saw_that, self, 'Passed null thisArg should be replaced with global object');
+
 }, 'HeaderMap in ServiceWorkerGlobalScope');
-