Implement Request.context for Fetch API

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

 if (self.importScripts) {
   importScripts('../resources/fetch-test-helpers.js');
 }
 
 var URL = 'https://www.example.com/test.html';
 
 function size(headers) {
   var count = 0;
   for (var header of headers) {
     ++count;
@@ skipping 697 matching lines @@
                            body: new Blob([''], {type: 'Text/Plain'}),
                            headers: [['Content-Type', 'Text/Html']]});
     req.body.cancel();
     return req.blob()
       .then(function(blob) {
           assert_equals(blob.type, 'text/html');
           assert_equals(req.headers.get('Content-Type'), 'Text/Html');
         });
   }, 'Extract a MIME type (2)');
 
+
+// Tests for requests context.
+promise_test(function(t) {
+    var req = new Request('http://localhost/',
+                          {method: 'POST', body: ''});
+    return req.blob()

[jsbell, 2015/04/06 17:04:15]

Extracting the body of the request here should not be necessary; unlike the
above tests for MIME/content-type this is just inspecting properties of the
Request.

It doesn't need to be an async promise_test either.

(Unless I'm radically misunderstanding the spec)

[shiva.jm, 2015/04/09 09:16:22]

Done.

+      .then(function(blob) {
+          assert_equals(req.context, '');

[jsbell, 2015/04/06 17:04:14]

Please add a message to the assertion, e.g. "RequestContext should be the empty
string for synthetic Request objects"

[shiva.jm, 2015/04/09 09:16:22]

Done.

+        });
+  }, 'requests context');

[jsbell, 2015/04/06 17:04:14]

Please give the test a more descriptive name, e.g. "RequestContext of a
synthetic Request object"

[shiva.jm, 2015/04/09 09:16:22]

Done.

+
+promise_test(function(t) {

[jsbell, 2015/04/06 17:04:14]

What is this test verifying that's different than the previous case?

[shiva.jm, 2015/04/09 09:16:22]

Done.

+    var req = new Request('http://localhost/',
+                          {method: 'POST',
+                           body: new Blob([''], {type: 'Text/Plain'}),
+                           headers: [['Content-Type', 'Text/Html']]});
+    return req.blob()
+      .then(function(blob) {
+          assert_equals(req.context, '');
+        });
+  }, 'requests context');
+
 done();