[polymer] Merge of master into polymer10-migration

netlog_viewer/assert.js

+// Copyright (c) 2013 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 Assertion support.
+ */
+
+/**
+ * Verify |condition| is truthy and return |condition| if so.
+ * @template T
+ * @param {T} condition A condition to check for truthiness.  Note that this
+ *     may be used to test whether a value is defined or not, and we don't want
+ *     to force a cast to Boolean.
+ * @param {string=} opt_message A message to show on failure.
+ * @return {T} A non-null |condition|.
+ */
+function assert(condition, opt_message) {
+  if (!condition) {
+    var message = 'Assertion failed';
+    if (opt_message)
+      message = message + ': ' + opt_message;
+    var error = new Error(message);
+    var global = function() { return this; }();
+    if (global.traceAssertionsForTesting)
+      console.warn(error.stack);
+    throw error;
+  }
+  return condition;
+}
+
+/**
+ * Call this from places in the code that should never be reached.
+ *
+ * For example, handling all the values of enum with a switch() like this:
+ *
+ *   function getValueFromEnum(enum) {
+ *     switch (enum) {
+ *       case ENUM_FIRST_OF_TWO:
+ *         return first
+ *       case ENUM_LAST_OF_TWO:
+ *         return last;
+ *     }
+ *     assertNotReached();
+ *     return document;
+ *   }
+ *
+ * This code should only be hit in the case of serious programmer error or
+ * unexpected input.
+ *
+ * @param {string=} opt_message A message to show when this is hit.
+ */
+function assertNotReached(opt_message) {
+  assert(false, opt_message || 'Unreachable code hit');
+}
+
+/**
+ * @param {*} value The value to check.
+ * @param {function(new: T, ...)} type A user-defined constructor.
+ * @param {string=} opt_message A message to show when this is hit.
+ * @return {T}
+ * @template T
+ */
+function assertInstanceof(value, type, opt_message) {
+  // We don't use assert immediately here so that we avoid constructing an error
+  // message if we don't have to.
+  if (!(value instanceof type)) {
+    assertNotReached(opt_message || 'Value ' + value +
+                     ' is not a[n] ' + (type.name || typeof type));
+  }
+  return value;
+}
+