Add histograms to entire MergeSession flow.

components/signin/core/browser/gaia_cookie_manager_service.cc

Index: components/signin/core/browser/gaia_cookie_manager_service.cc
diff --git a/components/signin/core/browser/gaia_cookie_manager_service.cc b/components/signin/core/browser/gaia_cookie_manager_service.cc
index 7eb1c283465c9d5ce76504a86f7973fc8bc04f0d..e6697887bd99437fdc34941148937e127df32b23 100644
--- a/components/signin/core/browser/gaia_cookie_manager_service.cc
+++ b/components/signin/core/browser/gaia_cookie_manager_service.cc
@@ -8,6 +8,7 @@
 #include <vector>
 
 #include "base/json/json_reader.h"
+#include "base/metrics/histogram_macros.h"
 #include "base/stl_util.h"
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
@@ -526,6 +527,8 @@ void GaiaCookieManagerService::OnMergeSessionFailure(
           << " error=" << error.ToString();
   if (++fetcher_retries_ < kMaxFetcherRetries && IsTransientError(error)) {
     fetcher_backoff_.InformOfRequest(false);
+    UMA_HISTOGRAM_ENUMERATION("OAuth2Login.MergeSessionRetry",
+        error.state(), GoogleServiceAuthError::NUM_STATES);
     fetcher_timer_.Start(
         FROM_HERE, fetcher_backoff_.GetTimeUntilRelease(),
         base::Bind(&SigninClient::DelayNetworkCall,
@@ -538,6 +541,9 @@ void GaiaCookieManagerService::OnMergeSessionFailure(
 
   uber_token_ = std::string();
   const std::string account_id = requests_.front().account_id();
+
+  UMA_HISTOGRAM_ENUMERATION("OAuth2Login.MergeSessionFailure",
+      error.state(), GoogleServiceAuthError::NUM_STATES);
   HandleNextRequest();
   SignalComplete(account_id, error);
 }
@@ -574,6 +580,8 @@ void GaiaCookieManagerService::OnListAccountsFailure(
          GaiaCookieRequestType::LIST_ACCOUNTS);
   if (++fetcher_retries_ < kMaxFetcherRetries && IsTransientError(error)) {
     fetcher_backoff_.InformOfRequest(false);
+    UMA_HISTOGRAM_ENUMERATION("Signin.ListAccountsRetry",
+        error.state(), GoogleServiceAuthError::NUM_STATES);
     fetcher_timer_.Start(
         FROM_HERE, fetcher_backoff_.GetTimeUntilRelease(),
         base::Bind(&SigninClient::DelayNetworkCall,
@@ -584,6 +592,8 @@ void GaiaCookieManagerService::OnListAccountsFailure(
     return;
   }
 
+  UMA_HISTOGRAM_ENUMERATION("Signin.ListAccountsFailure",
+      error.state(), GoogleServiceAuthError::NUM_STATES);
   FOR_EACH_OBSERVER(Observer, observer_list_,
       OnGaiaAccountsInCookieUpdated(listed_accounts_, error));
   HandleNextRequest();