Implement Request.context for Fetch API

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

Index: LayoutTests/http/tests/fetch/script-tests/fetch.js
diff --git a/LayoutTests/http/tests/fetch/script-tests/fetch.js b/LayoutTests/http/tests/fetch/script-tests/fetch.js
index caa2174f1aa5ab7c73d16b41ac3a35c603cce60e..b73e7e4efa9698b823d3560cb62b96a56545dc43 100644
--- a/LayoutTests/http/tests/fetch/script-tests/fetch.js
+++ b/LayoutTests/http/tests/fetch/script-tests/fetch.js
@@ -55,6 +55,7 @@ sequential_promise_test(function(t) {
     // serialized with the exclude fragment flag set.
     assert_equals(request.url,
       BASE_ORIGIN + '/serviceworker/resources/fetch-status.php?status=200');
+    assert_equals(request.context, '');
 
     return fetch(request)
       .then(function(response) {
@@ -66,6 +67,7 @@ sequential_promise_test(function(t) {
           assert_equals(response.url,
             BASE_ORIGIN +
             '/serviceworker/resources/fetch-status.php?status=200');
+          assert_equals(request.context, '');
         });
   }, 'Request/response url attribute getter with fragment');
 
@@ -79,6 +81,7 @@ sequential_promise_test(function(t) {
     var request = new Request(redirect_original_url);
     assert_equals(request.url, redirect_original_url,
       'Request\'s url is the original URL');
+    assert_equals(request.context, '');
 
     return fetch(request)
       .then(function(response) {
@@ -88,6 +91,7 @@ sequential_promise_test(function(t) {
             'Response\'s url is locationURL');
           assert_equals(request.url, redirect_original_url,
             'Request\'s url remains the original URL');
+          assert_equals(request.context, '');
         });
   }, 'Request/response url attribute getter with redirect');
 
@@ -106,12 +110,14 @@ sequential_promise_test(function(t) {
                     method: 'POST',
                     body: new Blob(['Test Blob'], {type: 'test/type'})
                   });
+    assert_equals(request.context, '');
     return fetch(request)
       .then(function(response) { return response.text(); })
       .then(evalJsonp)
       .then(function(result) {
           assert_equals(result.method, 'POST');
           assert_equals(result.body, 'Test Blob');
+          assert_equals(request.context, '');
         });
   }, 'Fetch with Blob body test');