[mojo] Enable ServiceRegistryImpl to override remote services

third_party/WebKit/LayoutTests/resources/mojo-helpers.js

Index: third_party/WebKit/LayoutTests/resources/mojo-helpers.js
diff --git a/third_party/WebKit/LayoutTests/resources/mojo-helpers.js b/third_party/WebKit/LayoutTests/resources/mojo-helpers.js
index 8752dd16989983ce2aea49bc3eaa26e35a1f4f8b..625d7fdfe46e06c320489bf8f8267644dfb9c658 100644
--- a/third_party/WebKit/LayoutTests/resources/mojo-helpers.js
+++ b/third_party/WebKit/LayoutTests/resources/mojo-helpers.js
@@ -35,3 +35,25 @@ function mojo_test(func, name, properties) {
     });
   }, name, properties);
 }
+
+// Polls aggressively for a message to become available on a pipe.
+function mojo_wait_for_incoming_message(mojo, pipe) {
+  return new Promise((resolve, reject) => {
+    let wait = () => {
+      let result = mojo.core.readMessage(pipe, 0);
+      if (result.result === mojo.core.RESULT_SHOULD_WAIT) {
+        setTimeout(wait);
+        return;
+      }
+
+      if (result.result !== mojo.core.RESULT_OK) {
+        reject(result.result);
+        return;
+      }
+
+      resolve({ buffer: result.buffer, handles: result.handles });
+    };
+
+    wait();
+  });
+};