Unify logic of stack trace generation for extension errors

extensions/renderer/resources/uncaught_exception_handler.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.
 
 // Handles uncaught exceptions thrown by extensions. By default this is to
 // log an error message, but tests may override this behaviour.
-
 var handler = function(message, e) {
   console.error(message);
 };
 
-// |message| The message associated with the error.
-// |e|       The object that was thrown.
-exports.handle = function(message, e) {
+/**
+ * Append the error description and stack trace to |message|.
+ *
+ * @param {string} message - The prefix of the error message.
+ * @param {Error|*} e - The thrown error object. This object is potentially
+ *   unsafe, because it could be generated by an extension.
+ * @param {string=} priorStackTrace - The stack trace to be appended to the
+ *   error message. This stack trace must not include stack frames of |e.stack|,
+ *   because both stack traces are concatenated. Overlapping stack traces will
+ *   confuse extension developers.
+ * @return {string} The formatted error message.
+ */
+function formatErrorMessage(message, e, priorStackTrace) {
+  if (e)
+    message += ': ' + safeErrorToString(e, false);
+
+  var stack;
+  try {
+    // If the stack was set, use it.
+    // |e.stack| could be void in the following common example:
+    // throw "Error message";
+    stack = $String.self(e && e.stack);
+  } catch (e) {}
+
+  // If a stack is not provided, capture a stack trace.
+  if (!priorStackTrace && !stack)
+    stack = getStackTrace();
+
+  stack = filterExtensionStackTrace(stack);
+  if (stack)
+    message += '\n' + stack;
+
+  // If an asynchronouse stack trace was set, append it.
+  if (priorStackTrace)
+    message += '\n' + priorStackTrace;
+
+  return message;
+}
+
+function filterExtensionStackTrace(stack) {
+  if (!stack)
+    return '';
+  // Remove stack frames in the stack trace that weren't associated with the
+  // extension, to not confuse extension developers with internal details.
+  stack = $String.split(stack, '\n');
+  stack = $Array.filter(stack, function(line) {
+    return $String.indexOf(line, 'chrome-extension://') >= 0;
+  });
+  return $Array.join(stack, '\n');
+}
+
+function getStackTrace() {
+  var e = {};
+  $Error.captureStackTrace(e, getStackTrace);
+  return e.stack;
+}
+
+function getExtensionStackTrace() {
+  return filterExtensionStackTrace(getStackTrace());
+}
+
+/**
+ * Convert an object to a string.
+ *
+ * @param {Error|*} e - A thrown object (possibly user-supplied).
+ * @param {boolean=} omitType - Whether to try to serialize |e.message| instead
+ *   of |e.toString()|.
+ * @return {string} The error message.
+ */
+function safeErrorToString(e, omitType) {
+  try {
+    return $String.self(omitType && e.message || e);
+  } catch (e) {
+    // This error is exceptional and could be triggered by
+    // throw {toString: function() { throw 'Haha' } };
+    return '(cannot get error message)';
+  }
+}
+
+/**
+ * Formats the error message and invokes the error handler.
+ *
+ * @param {string} message - Error message prefix.
+ * @param {Error|*} e - Thrown object.
+ * @param {string=} priorStackTrace - Error message suffix.
+ * @see formatErrorMessage
+ */
+exports.handle = function(message, e, priorStackTrace) {
+  message = formatErrorMessage(message, e, priorStackTrace);
   handler(message, e);
 };
 
-// |newHandler| A function which matches |exports.handle|.
+// |newHandler| A function which matches |handler|.
 exports.setHandler = function(newHandler) {
   handler = newHandler;
 };
+
+exports.getStackTrace = getStackTrace;
+exports.getExtensionStackTrace = getExtensionStackTrace;
+exports.safeErrorToString = safeErrorToString;