Stream blocks of timeline events over the service protocol

runtime/vm/service/service.md

 # Dart VM Service Protocol 3.3
 
 > Please post feedback to the [observatory-discuss group][discuss-list]
 
 This document describes of _version 3.3_ 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,
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 The _streamId_ parameter may have the following published values:
 
 streamId | event types provided
 -------- | -----------
 VM | VMUpdate
 Isolate | IsolateStart, IsolateRunnable, IsolateExit, IsolateUpdate, ServiceExtensionAdded
 Debug | PauseStart, PauseExit, PauseBreakpoint, PauseInterrupted, PauseException, Resume, BreakpointAdded, BreakpointResolved, BreakpointRemoved, Inspect
 GC | GC
 Extension | Extension
+Timeline | TimelineEvents
 
 Additionally, some embedders provide the _Stdout_ and _Stderr_
 streams.  These streams allow the client to subscribe to writes to
 stdout and stderr.
 
 streamId | event types provided
 -------- | -----------
 Stdout | WriteEvent
 Stderr | WriteEvent
 
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   InternalError,
 
   // The isolate has been terminated by an external source.
   TerminationError
 }
 ```
 
 ### Event
 
 ```
 class Event extends Response {

[turnidge, 2016/03/03 19:18:16]

Document the timelineEvents property here...

[Cutch, 2016/03/03 19:43:25]

Done.

   // What kind of event is this?
   EventKind kind;
 
   // The isolate with which this event is associated.
   //
   // This is provided for all event kinds except for:
   //   VMUpdate
   @Isolate isolate [optional];
 
   // The vm with which this event is associated.
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   // A garbage collection event.
   GC,
 
   // Notification of bytes written, for example, to stdout/stderr.
   WriteEvent,
 
   // Notification from dart:developer.inspect.
   Inspect,
 
   // Event from dart:developer.postEvent.
   Extension

[turnidge, 2016/03/03 19:18:16]

Add TimelineEvents here too?

The name TimelineEvents is a little funky... maybe Timeline?  Not sure.

[Cutch, 2016/03/03 19:43:25]

Stuck with TimelineEvents.

 }
 ```
 
 Adding new values to _EventKind_ is considered a backwards compatible
 change. Clients should ignore unrecognized events.
 
 ### ExtensionData
 
 ```
 class ExtensionData {
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 version | comments
 ------- | --------
 1.0 | initial revision
 2.0 | Describe protocol version 2.0.
 3.0 | Describe protocol version 3.0.  Added UnresolvedSourceLocation.  Added Sentinel return to getIsolate.  Add AddedBreakpointWithScriptUri.  Removed Isolate.entry. The type of VM.pid was changed from string to int.  Added VMUpdate events.  Add offset and count parameters to getObject() and offset and count fields to Instance. Added ServiceExtensionAdded event.
 3.1 | Add the getSourceReport RPC.  The getObject RPC now accepts offset and count for string objects.  String objects now contain length, offset, and count properties.
 3.2 | Isolate objects now include the runnable bit and many debugger related RPCs will return an error if executed on an isolate before it is runnable.
 3.3 | Pause event now indicates if the isolate is paused at an await, yield, or yield* suspension point via the 'atAsyncSuspension' field. Resume command now supports the step parameter 'OverAsyncSuspension'. A Breakpoint added synthetically by an 'OverAsyncSuspension' resume command identifies itself as such via the 'isSyntheticAsyncContinuation' field.
 
 [discuss-list]: https://groups.google.com/a/dartlang.org/forum/#!forum/observatory-discuss