Specs: fix typos in style2.md, checkin forgotten builtins.md, add guard feature to runloop.md, rena…

sky/specs/runloop.md

 Sky's Run Loop
 ==============
 
 Sky has three task queues, named idle, frame, and nextFrame.
 
 When a task is run, it has a time budget, and if the time budget is
 exceeded, then a catchable DeadlineExceededException exception is
 fired.
 
 ```dart
 class DeadlineExceededException implements Exception { }
 ```
 
+There is a method you can use that guards your code against these
+exceptions:
+
+```dart
+typedef void Callback();
+external guardAgainstDeadlineExceptions(Callback callback);
+// runs callback.
+// if the time budget for the _task_ expires while the callback is
+// running, the callback isn't interrupted, but the method will throw
+// an exception once the callback returns.
+```
+
 When Sky is to *process a task queue until a particular time*, with a
 queue *relevant task queue*, bits *filter bits*, a time
 *particular time*, and an *idle rule* which is either "sleep" or
 "abort", it must run the following steps:
 
 1. Let *remaining time* be the time until the given *particular time*.
 2. If *remaining time* is less than or equal to zero, exit this
    algorithm.
 3. Let *task list* be the list of tasks in the *relevant task queue*
    that have bits that, when 'and'ed with *filter bits*, are equal to
@@ skipping 99 matching lines @@
 int IdleKind = 0x01; // tasks that should run during the idle loop
 int LayoutKind = 0x02; // tasks that should run during layout
 int TouchSafeKind = 0x04; // tasks that should keep running while there is a pointer down
 int idleTaskBits = IdleKind; // tasks must have all these bits to run during idle loop
 int layoutTaskBits = LayoutKind; // tasks must have all these bits to run during layout
 
 // possible frame queue task bits
 // (there are none at this time)
 int frameTaskBits = 0x00; // tasks must have all these bits to run during the frame loop
 ```