Have FakeGCMProfileService return different registration IDs each time

chrome/browser/services/gcm/fake_gcm_profile_service.cc

Index: chrome/browser/services/gcm/fake_gcm_profile_service.cc
diff --git a/chrome/browser/services/gcm/fake_gcm_profile_service.cc b/chrome/browser/services/gcm/fake_gcm_profile_service.cc
index b5bdb17f1432151ac7b9509bea12d73500e59cb3..c2f05eda599ad38d7c3dde779ba1c889f6256490 100644
--- a/chrome/browser/services/gcm/fake_gcm_profile_service.cc
+++ b/chrome/browser/services/gcm/fake_gcm_profile_service.cc
@@ -111,7 +111,8 @@ KeyedService* FakeGCMProfileService::Build(content::BrowserContext* context) {
 }
 
 FakeGCMProfileService::FakeGCMProfileService(Profile* profile)
-    : collect_(false) {
+    : collect_(false),
+      registration_count_(0) {
   static_cast<PushMessagingServiceImpl*>(push_messaging_service())
       ->SetProfileForTesting(profile);
 }
@@ -126,11 +127,17 @@ void FakeGCMProfileService::RegisterFinished(
     last_registered_sender_ids_ = sender_ids;
   }
 
+  // Generate fake registration IDs with an incrementing count (even for the
+  // same app_id - there's no caching), so tests can distinguish registrations.
+  // The ID also encodes the number of sender IDs which is used by
+  // GcmApiTest.RegisterValidation, but in the most common case of a single
+  // sender ID, this component will be zero (to avoid rebasing existing tests).
+  int registration_id = ++registration_count_ + 1000 * (sender_ids.size() - 1);

[fgorski, 2014/12/08 22:36:59]

why not?
int registration_id = registration_count_ * 1000 + sender_ids.size();
++registration_count_;

I think it is ok to rebase failing tests in that case, but most of them should
stay the same.

[johnme, 2014/12/10 14:12:53]

Ok, I've changed it to a simpler format:
    sender_ids.size() + "-" + (registration_count_++)
and updated the tests.

+
   CustomFakeGCMDriver* custom_driver =
       static_cast<CustomFakeGCMDriver*>(driver());
-  custom_driver->OnRegisterFinished(app_id,
-                           base::UintToString(sender_ids.size()),
-                           GCMClient::SUCCESS);
+  custom_driver->OnRegisterFinished(app_id, base::IntToString(registration_id),
+                                    GCMClient::SUCCESS);
 }
 
 void FakeGCMProfileService::UnregisterFinished(const std::string& app_id) {