BodyStreamBuffer should take care the case where endRead returns Done

third_party/WebKit/LayoutTests/http/tests/fetch/script-tests/response.js

 if (self.importScripts) {
   importScripts('../resources/fetch-test-helpers.js');
   importScripts('/streams/resources/rs-utils.js');
 }
 
 function decode(chunks) {
   var decoder = new TextDecoder();
   var result = '';
   for (var chunk of chunks) {
     result += decoder.decode(chunk, {stream: true});
@@ skipping 472 matching lines @@
     assert_false(stream.locked);
     var response = new Response(stream);
     var p = response.text().then(t => {
         assert_equals(t, 'helloworld');
       });
     assert_true(stream.locked);
     return p;
   }, 'Response constructed with a stream');
 
 promise_test(() => {
+    var response = new Response('helloworld');
+    return readableStreamToArray(response.body).then(chunks => {
+        const decoder = new TextDecoder('utf-8');
+        let r = '';
+        for (const chunk of chunks) {
+          r += decoder.decode(chunk, {stream: true});
+        }
+        r += decoder.decode();
+        assert_equals(r, 'helloworld');
+      });
+  }, 'Response constructed with a String / Read from body stream');
+
+promise_test(() => {
     var controller;
     var stream = new ReadableStream({start: c => controller = c});
     controller.enqueue(new Uint8Array([0x68, 0x65, 0x6c, 0x6c, 0x6f]));
     controller.enqueue(new Uint8Array([0x77, 0x6f, 0x72, 0x6c, 0x64]));
     controller.close();
 
     var response = new Response(stream);
     return readableStreamToArray(response.body).then(chunks => {
         var decoder = new TextDecoder('utf-8');
         var r = '';
@@ skipping 43 matching lines @@
 
 promise_test(t => {
     var controller;
     var stream = new ReadableStream({start: c => controller = c});
     setTimeout(() => controller.enqueue('hello'), 1);
     var response = new Response(stream);
     return promise_rejects(t, TypeError(), response.text());
   }, 'Response constructed stream with a string chunk');
 
 done();