Bug 1692385 add some memory usage testing for setSinkId() r=pehrsons

Differential Revision: https://phabricator.services.mozilla.com/D106251

dom/media/webrtc/tests/mochitests/head.js

@@ -892,6 +892,36 @@ function haveEventsButNoMore(target, name, count, cancel) {
   );
 }
 
+/*
+ * Resolves the returned promise with an object with usage and reportCount
+ * properties.  `usage` is in the same units as reported by the reporter for
+ * `path`.
+ */
+const collectMemoryUsage = async path => {
+  const MemoryReporterManager = Cc[
+    "@mozilla.org/memory-reporter-manager;1"
+  ].getService(Ci.nsIMemoryReporterManager);
+
+  let usage = 0;
+  let reportCount = 0;
+  await new Promise(resolve =>
+    MemoryReporterManager.getReports(
+      (aProcess, aPath, aKind, aUnits, aAmount, aDesc) => {
+        if (aPath != path) {
+          return;
+        }
+        ++reportCount;
+        usage += aAmount;
+      },
+      null,
+      resolve,
+      null,
+      /* anonymized = */ false
+    )
+  );
+  return { usage, reportCount };
+};
+
 /**
  * This class executes a series of functions in a continuous sequence.
  * Promise-bearing functions are executed after the previous promise completes.

dom/media/webrtc/tests/mochitests/test_setSinkId.html

@@ -12,6 +12,8 @@
     bug: "934425",
   });
 
+  const memoryReportPath = 'explicit/media/media-manager-aggregates';
+
   /**
    * Run a test to verify set sink id in audio element.
    */
@@ -48,6 +50,28 @@
       ok(true, `Set sink id expected to fail: ${error}`);
       is(error.name, "NotFoundError", "Verify correct error");
     }
+
+    const {usage: usage1} =
+          await collectMemoryUsage(memoryReportPath); // Provided by head.js
+
+    ok(usage1 > 0, "MediaManager memory usage should be non-zero to store \
+device ids after enumerateDevices");
+
+    const p2 = audio.setSinkId("");
+    is(audio.sinkId, audioDevices[0].deviceId,
+       'sinkId after setSinkId("") return');
+    is(await p2, undefined,
+       "promise resolution value when sinkId parameter is empty");
+    is(audio.sinkId, "", 'sinkId after setSinkId("") resolution');
+
+    await audio.setSinkId(audioDevices[0].deviceId);
+
+    const {usage: usage2, reportCount} =
+          await collectMemoryUsage(memoryReportPath);
+    is(reportCount, 1,
+       'Expect only one MediaManager to report in content processes.');
+    is(usage2, usage1, "MediaManager memory usage should return to previous \
+value after promise resolution");
   });
 
 </script>