Chrome extension to get console messages upon test failures. Unlike the

tools/testing/extensions/chrome/ConsoleCollector/background.js

+// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/**
+ * This is the background window. It can access the necessary APIs to get
+ * at the console messages. It can only communicate with the content
+ * window through message passing.
+ *
+ * There is no way to query the console messages, as such, but we can
+ * set up a handler that is called when there are console messages. This 
+ * will be called with any console messages already present, so it can be set
+ * up after the fact. However, if there are no messages it won't be called.
+ * To handle the end of the messages (or no messages) we have to use a 
+ * sentinel message that is logged by the content page.
+ */
+var version = "1.0";
+var messages = []; // An array that we can put messages in.
+var debuggeeId; // An object that identifies the browser tab we are talking to.
+var callback; // For passing back the response to the content window.
+var timer; // To time out if no messages are available.
+
+/**
+ * When we have collected all the messages, we send them back to the
+ * content page via the callback, turn off message collection, and
+ * detach the debugger from the browser tab.
+ */
+function allDone() {
+  callback(messages); 
+  chrome.debugger.sendCommand(debuggeeId, "Console.clearMessages", {},
+      function() {
+        chrome.debugger.sendCommand(debuggeeId, "Console.disable", {},
+            function() {});
+        chrome.debugger.detach(debuggeeId, function() {});
+  });
+  messages = [];
+}
+
+/**
+ * Debugger event handler. We only care about console.messageAdded
+ * events, in which case we add a new message object with the fields
+ * we care about to our messages array.
+ */
+function onEvent(debuggeeId, method, params) {
+  var tabId = debuggeeId.tabId;
+  if (method == "Console.messageAdded") {
+    var msg = params.message;
+    // More fields are available if we want them later. See
+    // https://developers.google.com/chrome-developer-tools/docs/protocol/1.0/console#type-ConsoleMessage
+    if (msg.text == 'getMessages/end') {
+      allDone();
+    } else {
+      messages.push({"source":msg.url, "line": msg.line,
+          "category":msg.source, "message":msg.text });
+    }
+  }
+}
+
+/**
+ * Handle requests sent by the content script. We save the callback,
+ * get the window and tab that is currently active, attach the 
+ * debugger to that tab, and then turn on console message event 
+ * handling, which will result in onEvent calls for each console 
+ * message, including the ones that are already present in the console.
+ */
+function onRequest(request, sender, sendResponse) {
+  if (request.command == "getMessages") {
+    callback = sendResponse;
+    chrome.windows.getCurrent(function(win) {
+      chrome.tabs.getSelected(win.id, function(tab) {
+        debuggeeId = {tabId:tab.id};
+        chrome.debugger.attach(debuggeeId, version, function() {
+          if (chrome.extension.lastError) {
+            // Attach failed; send an empty response.
+            callback([]);
+          } else {
+            chrome.debugger.sendCommand(debuggeeId, "Console.enable", {},
+              function() {});
+            //timer = setTimeout(allDone, 1000);
+          }
+        });
+      });
+    });
+  }
+}
+
+// Set up the general handler for debug events.
+chrome.debugger.onEvent.addListener(onEvent);
+// Listen for the content script to send a message to the background page.
+chrome.extension.onRequest.addListener(onRequest);