Add CORS headers to URLRequestRedirectJob.

chrome/test/data/extensions/api_test/webrequest/cors/load_image.html

+<script>
+var img = document.createElement('img');
+img.crossOrigin = location.search.match(/crossOrigin=(anonymous|use-credentials)/)[1];
+
+// After verifying that the image is loaded correctly, we
+// must also check whether the renderer accepts the resource.
+// The replies are delayed to allow tests to close the tabs in case
+// the test failed at an early stage.
+img.onerror = function() {
+    setTimeout(function() {
+        // Should not happen. Failure is signaled to allow the unit tests to continue
+        // with the next test, the exact value of the next string does not matter.
+        new Image().src = '/signal_that_image_failed_to_load';
+    }, 500);
+};
+img.onload = function() {
+    setTimeout(function() {
+        // Verified in test_blocking.js
+        new Image().src = '/signal_that_image_loaded_successfully';
+    }, 500);
+};
+
+img.src = decodeURIComponent(location.search.match(/src=([^&]+)/)[1]);
+</script>