[mojo] Enable ServiceRegistryImpl to override remote services

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

 /*
  * mojo-helpers contains extensions to testharness.js useful for consuming
  * and mocking Mojo services directly within test code.
  */
 'use strict';
 
 // Runs a promise_test which depends on the Mojo system API modules available to
 // all layout tests. The test implementation function is called with an Object
 // that exposes common Mojo module interfaces.
 function mojo_test(func, name, properties) {
@@ skipping 17 matching lines @@
             // called |serviceRegistry|, so let's call it that here.
             serviceRegistry: serviceProvider,
           }));
         } catch (e) {
           reject(e);
         }
       });
     });
   }, 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();
+  });
+};