add optional request field to record time at which client made request

pkg/analysis_server/tool/spec/spec_input.html

Index: pkg/analysis_server/tool/spec/spec_input.html
diff --git a/pkg/analysis_server/tool/spec/spec_input.html b/pkg/analysis_server/tool/spec/spec_input.html
index ad1421d1c16e74f501a686a957584289c4a8dff7..a74e92b64aa0f58e8a285d74ff20e65649a74a17 100644
--- a/pkg/analysis_server/tool/spec/spec_input.html
+++ b/pkg/analysis_server/tool/spec/spec_input.html
@@ -58,15 +58,18 @@
       longer to process than others.
     </p>
     <p>
-      Every request is required to have two fields and may have an
-      optional third field. The first required field is the ‘id’
+      Every request is required to have two fields and may have two
+      additional optional fields. The first required field is the ‘id’
       field, which is only used by the server to associate a response
       with the request that generated the response. The second
       required field is the ‘method’ field, which is used to determine
-      what the server is being requested to do. The optional field is
+      what the server is being requested to do. One optional field is
       the ‘params’ field, whose structure is dependent on the method
       being requested. The structure of this field is described with
-      each request for which it is required.
+      each request for which it is required. The other optional field
+      is the 'clientRequestTime' field, which is a number indicating
+      the time at which the client made the request (milliseconds
+      since epoch).

[Brian Wilkerson, 2015/01/23 14:57:20]

We should explain what the value is used for in order to motivate clients to
provide the value.

[danrubel, 2015/01/23 16:00:43]

Good point. Done.

     </p>
     <p>
       Every response has up to three fields. The first field is the