MediaPerceptionPrivate API impl and testing.

extensions/test/data/media_perception_private/media_perception/runtest.js

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Set the state to STARTED to automatically start listening to
+// MediaPerceptionDetection signals.
+
+chrome.test.runTests([
+    function setStateRunning() {
+      // Need to start the mocked media analytics process.
+      chrome.mediaPerceptionPrivate.setState({
+        status: 'RUNNING'
+      }, chrome.test.callbackPass(function(state) {
+        chrome.test.assertEq(state.status, 'RUNNING');
+      }));
+    },
+    function registerListener() {
+      chrome.test.listenOnce(
+          chrome.mediaPerceptionPrivate.onMediaPerception,
+          function(evt) {
+            chrome.test.assertEq(evt.framePerceptions[0].frameId, 1);
+          });
+      // By sending this message, we trigger the fake D-Bus client to fire an
+      // onMediaPerception event.
+      chrome.test.sendMessage('mediaPerceptionListenerSet');
+    }
+]);
+