Add multi_profile_user_count field to system_profile proto.

chrome/common/metrics/proto/system_profile.proto

Index: chrome/common/metrics/proto/system_profile.proto
diff --git a/chrome/common/metrics/proto/system_profile.proto b/chrome/common/metrics/proto/system_profile.proto
index 65940aba5a3b5bfada4eabfc3c75bb768b7c0f10..38ca1aec93afdf254db0effa5e7f094f0a6d8527 100644
--- a/chrome/common/metrics/proto/system_profile.proto
+++ b/chrome/common/metrics/proto/system_profile.proto
@@ -11,7 +11,7 @@ option optimize_for = LITE_RUNTIME;
 
 package metrics;
 
-// Next tag: 17
+// Next tag: 18
 message SystemProfileProto {
   // The time when the client was compiled/linked, in seconds since the epoch.
   optional int64 build_timestamp = 1;
@@ -319,7 +319,7 @@ message SystemProfileProto {
     // If a client has multiple local Chrome user accounts, this is logged based
     // on the first user account launched during the current session.
     optional bool is_disabled = 4;
-    
+
     // True if the plugin is PPAPI.
     optional bool is_pepper = 5;
   }
@@ -437,4 +437,9 @@ message SystemProfileProto {
     optional fixed32 group_id = 2;
   }
   repeated FieldTrial field_trial = 9;
+
+  // Number of users currently signed into a multiprofile session.
+  // Non-positive values indicates that the count is unknown or ambiguous.
+  // Logged only on ChromeOS.
+  optional int32 multi_profile_user_count = 17;

[Ilya Sherman, 2013/09/30 23:42:52]

Can this be an unsigned field?  If not, please document what the semantics of
distinct non-positive values are.

[Tim Song, 2013/10/05 01:25:23]

Done. I wanted to leave open the possibility of using negative values to
indicate the number of users when the log is invalidated, but I don't think this
would be really useful. 

 }