Implement Request.context for Fetch API

LayoutTests/http/tests/fetch/script-tests/request.js

Index: LayoutTests/http/tests/fetch/script-tests/request.js
diff --git a/LayoutTests/http/tests/fetch/script-tests/request.js b/LayoutTests/http/tests/fetch/script-tests/request.js
index 1f736874cf3220723030df931858383b83f64ee1..0d27bd37e0e86b98bdd9805b3b47b10e2a9fb9ff 100644
--- a/LayoutTests/http/tests/fetch/script-tests/request.js
+++ b/LayoutTests/http/tests/fetch/script-tests/request.js
@@ -715,4 +715,11 @@ promise_test(function(t) {
         });
   }, 'Extract a MIME type (2)');
 
+// Tests for requests context.
+test(function() {
+    var request = new Request('http://localhost/', {method: 'POST', body: ''});
+    assert_equals(request.context, '',
+                  'Request.context should be empty string for synthetic Request object');

[hiroshige, 2015/04/09 17:43:21]

nit: please wrap to 80 columns, e.g.
                  'Request.context should be empty string ' +
                  'for synthetic Request object');
(https://www.chromium.org/blink/serviceworker/testing#TOC-Layout-Tests-Style)

[shiva.jm, 2015/04/10 09:27:10]

Done.

+  }, 'RequestContext of a synthetic Request object');
+
 done();