Provide list of service protocol extensions in isolate and emit an event when one is registered

runtime/vm/service/service.md

Index: runtime/vm/service/service.md
diff --git a/runtime/vm/service/service.md b/runtime/vm/service/service.md
index e71169d8334b1d9582eb1df76d12c68349a63bbc..2c72b725b89419871b69c1a4d39c385a658a6af7 100644
--- a/runtime/vm/service/service.md
+++ b/runtime/vm/service/service.md
@@ -715,7 +715,7 @@ The _streamId_ parameter may have the following published values:
 streamId | event types provided
 -------- | -----------
 VM | VMUpdate
-Isolate | IsolateStart, IsolateRunnable, IsolateExit, IsolateUpdate
+Isolate | IsolateStart, IsolateRunnable, IsolateExit, IsolateUpdate, ServiceExtensionAdded
 Debug | PauseStart, PauseExit, PauseBreakpoint, PauseInterrupted, PauseException, Resume, BreakpointAdded, BreakpointResolved, BreakpointRemoved, Inspect
 GC | GC
 
@@ -1139,6 +1139,11 @@ class Event extends Response {
   //
   // This is provided for the Inspect event.
   @Instance inspectee [optional];
+
+  // The RPC name of the extension that was added.
+  //
+  // This is provided for the ServiceExtensionAdded.
+  string extensionRPC [optional];
 }
 ```
 
@@ -1170,6 +1175,9 @@ enum EventKind {
   // via setName.
   IsolateUpdate,
 
+  // Notification that an extension RPC was registered on an isolate.
+  ServiceExtensionAdded,
+
   // An isolate has paused at start, before executing code.
   PauseStart,
 
@@ -1815,6 +1823,9 @@ class Isolate extends Response {
 
   // The current pause on exception mode for this isolate.
   ExceptionPauseMode exceptionPauseMode;
+
+  // The list of service extension RPCs that are registered for this isolate.
+  string[] extensionRPCs;
 }
 ```
 
@@ -2281,7 +2292,7 @@ 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.
+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.
 
 
 [discuss-list]: https://groups.google.com/a/dartlang.org/forum/#!forum/observatory-discuss