Add the ability to run tests with several sets of VM flags

runtime/tests/dart/src/EchoServerStreamReadUntilTest.dart

Index: runtime/tests/dart/src/EchoServerStreamReadUntilTest.dart
diff --git a/runtime/tests/dart/src/EchoServerStreamReadUntilTest.dart b/runtime/tests/dart/src/EchoServerStreamReadUntilTest.dart
index e8df2282668230572adde6a9bc793a730bbfa616..cca1ed53ea9ce04bc2565063622d7c8b1dc53275 100644
--- a/runtime/tests/dart/src/EchoServerStreamReadUntilTest.dart
+++ b/runtime/tests/dart/src/EchoServerStreamReadUntilTest.dart
@@ -3,6 +3,11 @@
 // BSD-style license that can be found in the LICENSE file.
 //
 // Echo server test program to test socket stream read until functionality.
+//
+// VMOptions=
+// VMOptions=--short_socket_read
+// VMOptions=--short_socket_write
+// VMOptions=--short_socket_read --short_socket_write
 
 main() {
   EchoServerStreamReadUntilTest.testMain();
@@ -146,12 +151,16 @@ class EchoServer extends Isolate {
             for (int i = 0; i < MSGSIZE - 1; i++) {
               Expect.equals(EchoServerGame.FIRSTCHAR + i, buffer[i]);
             }
-            outputStream.write(buffer, 0, buffer.length, null);
-            inputStream.readUntil(PATTERN2, dataReceived);
+            void next() {
+              inputStream.readUntil(PATTERN2, dataReceived);
+            }
+            bool done = outputStream.write(buffer, 0, buffer.length, next);
+            if (done) {
+              next();
+            }
           } else {
             Expect.equals(1, buffer.length);
             outputStream.write(buffer, 0, buffer.length, null);
-            inputStream.readUntil(PATTERN2, dataReceived);
           }
         }