Remember when an isolate was paused and subtly display it in Obseravatory

runtime/vm/service/service.md

 # Dart VM Service Protocol 2.0
 
 > Please post feedback to the [observatory-discuss group][discuss-list]
 
 This document describes of _version 2.0_ of the Dart VM Service Protocol. This
 protocol is used to communicate with a running Dart Virtual Machine.
 
 To use the Service Protocol, start the VM with the *--observe* flag.
 The VM will start a webserver which services protocol requests via WebSocket.
 It is possible to make HTTP (non-WebSocket) requests,
@@ skipping 941 matching lines @@
 ### Event
 
 ```
 class Event extends Response {
   // What kind of event is this?
   EventKind kind;
 
   // The isolate with which this event is associated.
   @Isolate isolate;
 
+  // The timestamp (in milliseconds since the epoch) associated with this event.
+  // For some isolate pause events, the timestamp is from when the isolate was
+  // paused. For other events, the timestamp is from when the event was created.

[nweiz, 2015/09/10 22:45:13]

Which events are which?

+  int timestamp;
+
   // The breakpoint which was added, removed, or resolved.
   //
   // This is provided for the event kinds:
   //   PauseBreakpoint
   //   BreakpointAdded
   //   BreakpointRemoved
   //   BreakpointResolved
   Breakpoint breakpoint [optional];
 
   // The list of breakpoints at which we are currently paused
@@ skipping 1027 matching lines @@
 ```
 
 ## Revision History
 
 version | comments
 ------- | --------
 1.0 draft 1 | initial revision
 
 
 [discuss-list]: https://groups.google.com/a/dartlang.org/forum/#!forum/observatory-discuss