Add a Record button to the web-app if the host supports video recording.

remoting/webapp/video_frame_recorder.js

+// Copyright 2014 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.
+
+/**
+ * @fileoverview
+ * Class implement the video frame recorder extension client.

[Jamie, 2014/08/19 00:48:56]

s/implement/implementing/

+ */
+
+'use strict';
+
+/** @suppress {duplicate} */
+var remoting = remoting || {};
+
+/**
+ * @constructor
+ */
+remoting.VideoFrameRecorder = function(plugin) {
+  this.fileWriter_ = null;
+  this.isRecording_ = false;
+  this.plugin_ = plugin;
+};
+
+/**
+ *
+ */
+remoting.VideoFrameRecorder.prototype.startStopRecording = function() {
+  var data = {};
+  if (this.isRecording_) {
+    this.isRecording_ = false;
+    data = { type: 'stop' }
+
+    chrome.fileSystem.chooseEntry(
+        {type: 'saveFile', suggestedName: "videoRecording.pb"},

[Jamie, 2014/08/19 00:48:56]

You've used padding spaces after '{' and before '}' elsewhere in this file.

+        this.onFileChosen_.bind(this));
+  } else {
+    this.isRecording_ = true;
+    data = { type: 'start' }
+  }
+  this.plugin_.sendClientMessage('video-recorder', JSON.stringify(data));
+}
+
+/**
+ *
+ */
+remoting.VideoFrameRecorder.prototype.onFileChosen_ = function(fileEntry) {
+  if (!fileEntry) {
+    console.log("Cancelled save of video frames.");
+  } else {
+    chrome.fileSystem.getDisplayPath(fileEntry, function(path) {
+      console.log("Saving video frames to:" + path);
+    });
+    fileEntry.createWriter(this.onFileWriter_.bind(this));
+  }
+}
+
+/**
+ *
+ */
+remoting.VideoFrameRecorder.prototype.onFileWriter_ = function(fileWriter) {
+  console.log("Obtained FileWriter for video frame write");
+  fileWriter.onwriteend = this.onWriteComplete_.bind(this);

[Jamie, 2014/08/19 00:48:56]

Do you need an onerror handler?

+  this.fileWriter_ = fileWriter;
+  this.fetchNextFrame_();
+}
+
+/*
+ *
+ */
+remoting.VideoFrameRecorder.prototype.onWriteComplete_ = function(e) {

[Jamie, 2014/08/19 00:48:56]

In JS, there's no need to declare parameters if you're not using them. If you do
want to declare it, please give it a more descriptive name.

+  console.log("Video frame write complete");
+  this.fetchNextFrame_();
+}
+
+/*
+ *
+ */
+remoting.VideoFrameRecorder.prototype.fetchNextFrame_ = function() {
+  console.log("Request next video frame");
+  var data = { type: 'next-frame' }
+  this.plugin_.sendClientMessage('video-recorder', JSON.stringify(data));
+}
+
+/**
+ *
+ */
+remoting.VideoFrameRecorder.prototype.handleMessage =
+    function(type, data) {
+  if (type != 'video-recorder') {
+    return false;
+  }
+
+  var message = getJsonObjectFromString(data);
+
+  if (message.type == 'next-frame-reply') {
+    if (!this.fileWriter_) {
+      console.log("Received frame but have no writer");
+      return true;
+    }
+    if (!message.data) {
+      console.log("Finished receiving frames");
+      this.fileWriter_ = null;
+      return true;
+    }
+
+    console.log("Received frame");
+    var videoPacketString = atob(message.data);
+
+    console.log("Converted from Base64 - length:" + videoPacketString.length);
+    var byteArrays = [];
+
+    for (var offset = 0; offset < videoPacketString.length; offset += 512) {
+        var slice = videoPacketString.slice(offset, offset + 512);

[Jamie, 2014/08/19 00:48:56]

Indentation.

+        var byteNumbers = new Array(slice.length);
+        for (var i = 0; i < slice.length; i++) {
+            byteNumbers[i] = slice.charCodeAt(i);
+        }

[Jamie, 2014/08/19 00:48:56]

Can you do this more succinctly with Array.map?

+        var byteArray = new Uint8Array(byteNumbers);
+        byteArrays.push(byteArray);
+    }
+
+    console.log("Writing frame");
+    videoPacketString = null;
+    var videoPacketBlob = new Blob(byteArrays);
+    byteArrays = null;
+
+    this.fileWriter_.write(videoPacketBlob);
+
+    return true;
+  }
+
+  console.log("Unrecognized message: " + message.type);
+  return true;
+}