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, None
 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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   // The extension event kind.
   //
   // This is provided for the Extension event.
   string extensionKind [optional];
 
   // The extension event data.
   //
   // This is provided for the Extension event.
   ExtensionData extensionData [optional];
 
+  // An array of TimelineEvents
+  //
+  // This is provided for the TimelineEvents event.
+  TimelineEvent[] timelineEvents [optional];
+
   // Is the isolate paused at an await, yield, or yield* statement?
   //
   // This is provided for the event kinds:
   //   PauseBreakpoint
   //   PauseInterrupted
   bool atAsyncSuspension [optional];
 }
 ```
 
 An _Event_ is an asynchronous notification from the VM. It is delivered
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 ### Success
 
 ```
 class Success extends Response {
 }
 ```
 
 The _Success_ type is used to indicate that an operation completed successfully.
 
+### TimelineEvent
+
+```
+class TimelineEvent {
+}
+```
+
+An _TimelineEvent_ is an arbitrary map that contains a [Trace Event Format](https://docs.google.com/document/d/1CvAClvFfyA5R-PhYUmn5OOQtYMH4h6I0nSsKchNAySU/preview) event.
+
 ### TypeArguments
 
 ```
 class @TypeArguments extends @Object {
   // A name for this type argument list.
   string name;
 }
 ```
 
 _@TypeArguments_ is a reference to a _TypeArguments_ object.
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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