Return an error in many service RPCs if the isolate is not runnable

runtime/vm/service/service.md

 # Dart VM Service Protocol 3.0
 
 > Please post feedback to the [observatory-discuss group][discuss-list]
 
 This document describes of _version 3.0_ 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,
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 In addition the the [error codes](http://www.jsonrpc.org/specification#error_object)
 specified in the JSON-RPC spec, we use the following application specific error codes:
 
 code | message | meaning
 ---- | ------- | -------
 100 | Feature is disabled | The operation is unable to complete because a feature is disabled
 101 | VM must be paused | This operation is only valid when the VM is paused
 102 | Cannot add breakpoint | The VM is unable to add a breakpoint at the specified line or function
 103 | Stream already subscribed | The client is already subscribed to the specified _streamId_
 104 | Stream not subscribed | The client is not subscribed to the specified _streamId_
+105 | Isolate must be runnable | This operation cannot happen until the isolate is runnable
 
 
 
 
 ## Events
 
 By using the [streamListen](#streamlisten) and [streamCancel](#streamcancel) RPCs, a client may
 request to be notified when an _event_ is posted to a specific
 _stream_ in the VM. Every stream has an associated _stream id_ which
 is used to name that stream.
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 ## Revision History
 
 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.
 
 
 [discuss-list]: https://groups.google.com/a/dartlang.org/forum/#!forum/observatory-discuss