Have FakeGCMProfileService return different registration IDs each time

chrome/test/data/extensions/api_test/gcm/functions/register_validation/register_validation.js

Index: chrome/test/data/extensions/api_test/gcm/functions/register_validation/register_validation.js
diff --git a/chrome/test/data/extensions/api_test/gcm/functions/register_validation/register_validation.js b/chrome/test/data/extensions/api_test/gcm/functions/register_validation/register_validation.js
index 952769f967f14d6899e9801b2b1cf47ba576fd0b..f64c2399004246f6cce669b8019dc6a4ed111017 100644
--- a/chrome/test/data/extensions/api_test/gcm/functions/register_validation/register_validation.js
+++ b/chrome/test/data/extensions/api_test/gcm/functions/register_validation/register_validation.js
@@ -20,9 +20,12 @@ function toArrayDefinitionString(senderIds) {
   return idsString;
 }
 
+var registrationCount = 0;
+
 function registerSuccessfully(senderIds) {
   chrome.gcm.register(senderIds, function(registrationId) {
-    chrome.test.assertEq("" + senderIds.length, registrationId);
+    var expectedRegistrationId = senderIds.length + "-" + (registrationCount++);
+    chrome.test.assertEq("" + expectedRegistrationId, registrationId);
     chrome.test.succeed();
   });
 }