Ensure that service protocol specification and implementation use the correct numeric types

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,
@@ skipping 2111 matching lines @@
   // The CPU we are generating code for.
   string targetCPU;
 
   // The CPU we are actually running on.
   string hostCPU;
 
   // The Dart VM version string.
   string version;
 
   // The process id for the VM.
-  string pid;
+  int pid;
 
   // The time that the VM started in milliseconds since the epoch.
   //
   // Suitable to pass to DateTime.fromMillisecondsSinceEpoch.
   int startTime;
 
   // A list of isolates running in the VM.
   @Isolate[] isolates;
 }
 ```
 
 ## 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.
+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.
 
 
 [discuss-list]: https://groups.google.com/a/dartlang.org/forum/#!forum/observatory-discuss