MediaPerceptionPrivate API impl and testing.

chrome/test/data/extensions/api_test/media_perception_private/diagnostics/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.
+
+chrome.test.runTests([
+    function getDiagnostics() {
+      // Need to start the mocked media analytics process.
+      chrome.mediaPerceptionPrivate.setState(

[tbarzic, 2017/05/11 00:38:27]

can you move this to another test, to make sure getDiagnostics does not get
called before the state callback is invoked?

also, reformat this as:
chrome.mediaPerceptionPrivate.setState({
  status: 'RUNNING'
}, chrome.testCallbackPass(function(state) {

}))

[Luke Sorenson, 2017/05/11 23:57:58]

Done.

+          { status: 'RUNNING' }, chrome.test.callbackPass(function(state) {
+            chrome.test.assertEq(state.status, 'RUNNING');
+          }));
+      chrome.mediaPerceptionPrivate.getDiagnostics(
+          chrome.test.callbackPass(function(response) {
+            chrome.test.assertEq(
+                response.perceptionSamples[0].framePerception.frameId, 1);
+          }));
+    }
+]);