Hook up PA_LOG() logs to chrome://proximity-auth WebUI.

components/proximity_auth/webui/resources/log-buffer.js

+// Copyright 2015 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.
+
+Polymer('log-buffer', {
+  publish: {
+    /**
+     * List of displayed logs.
+     * @type {?Array.<{{
+     *    text: string,
+     *    time: string,
+     *    file: string,
+     *    line: number,
+     *    severity: number,
+     * }}>} LogMessage
+     */
+    logs: null,
+  },
+
+  /**
+   * Called when an instance is created.
+   */
+  created: function() {
+    this.logs = [];
+    // We assume that only one instance of log-buffer is ever created.
+    LogBufferInterface = this;
+    chrome.send('getLogMessages');
+  },
+
+  // Clears the native LogBuffer.
+  clearLogs: function() {
+    chrome.send('clearLogBuffer');
+  },
+
+  // Handles when a new log message is added.
+  onLogMessageAdded: function(log) {
+    this.logs.push(log);
+  },
+
+  // Handles when the logs are cleared.
+  onLogBufferCleared: function() {
+    this.logs = [];
+  },
+
+  // Handles when the logs are returned in response to the 'getLogMessages'
+  // request.
+  onGotLogMessages: function(logs) {
+    this.logs = logs;
+  }
+});
+
+// Interface with the native WebUI component for LogBuffer events.
+// The functions contained in this object will be invoked by the browser when
+// for each operation performed on the native LogBuffer.

[Ilya Sherman, 2015/05/13 00:49:57]

nit: "when for each" -> "for each"?

[Tim Song, 2015/05/13 02:24:37]

Done.

+LogBufferInterface = {
+  /**
+   * Called when a new log message is added.
+   * @type {function(LogMessage)}
+   */
+  onLogMessageAdded: function(log) {},
+
+  /**
+   * Called when the log buffer is cleared.
+   * @type {function()}
+   */
+  onLogBufferCleared: function() {},
+
+  /**
+   * Called in response to chrome.send('getLogMessages') with the log messages
+   * currently in the buffer.
+   * @type {function(Array.<LogMessage>)}
+   */
+  onGotLogMessages: function(messages) {},
+};