error-reporting: Fix report() silently failing (#2363)

* error-reporting: Fix `report()` silently failing

If the `report()` method is called with a number, an associated
error never appears in the error reporting console, and no log
message is printed to the user to indicate why the error has not
appeared.

* Fix linting errors

* Add the new `build-stack-trace.js` file

* Add more system tests for `errors.report()`

* Rename errorHandlerRouter to populateErrorMessage

* Rename error-router to populate-error-message

* Reorganize the populate-error-message tests

* Update buildStackTrace to use captureStackTrace

The `Error.captureStackTrace` method is now used in the
`buildStackTrace` function to create a stack trace.

* Simplify the system tests

The code for verifiying that stack traces don't contain
error-reporting specific frames has been consolidated into a
single location.

* Consolidate code in populate-error-message.js

* Make the `buildStackTrace` more robust

In particular, the `buildStackTrace` was updated to ensure that
no error-reporting specific frames are included in the built
stack trace.  In addition, the system-tests have been updated to
ensure error-reporting related frames, and only those frames, are
removed from the built stack trace.

packages/error-reporting/src/build-stack-trace.js

@@ -0,0 +1,42 @@
+/**
+ * Copyright 2017 Google Inc. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+'use strict';
+
+const SRC_ROOT = __dirname;
+
+/**
+ * Constructs a string representation of the stack trace at the point where
+ * this function was invoked.  Note that the stack trace will not include any
+ * references to frames specific to this error-reporting library itself.
+ * @param {String?} message - The message that should appear as the first line
+ *   of the stack trace.  This value defaults to the empty string.
+ * @returns {String} - A string representation of the stack trace at the point
+ *   where this method was invoked.
+ */
+function buildStackTrace(message) {
+  var target = {};
+  // Build a stack trace without the frames associated with `buildStackTrace`.
+  // The stack is located at `target.stack`.
+  Error.captureStackTrace(target, buildStackTrace);
+  var prefix = message ? message + '\n' : '';
+  return prefix + target.stack.split('\n').slice(1).filter(function(line) {
+    // Filter out all frames that are specific to the error-reporting library
+    return !line || line.indexOf(SRC_ROOT) === -1;
+  }).join('\n');
+}
+
+module.exports = buildStackTrace;