When there is more than one username mapping for the cloud identity user, GCPW falls back to

new account creation irrespective of whether both those user mappings exist on the device.
We should instead fallback to new user creation only if we have multiple valid user mappings
on the device.

Bug: 1137547
Change-Id: I9924a3b07235a05472f35998fb5be869c43d83c1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2465584
Commit-Queue: Rakesh Soma <rakeshsoma@google.com>
Reviewed-by: Yusuf Sengul <yusufsn@google.com>
Cr-Commit-Position: refs/heads/master@{#816695}

chrome/credential_provider/gaiacp/gaia_credential_base.cc

@@ -247,9 +247,11 @@ HRESULT GetUserAndDomainInfo(
     BSTR* error_text) {
   base::string16 user_name;
   base::string16 domain_name;
+  OSUserManager* os_user_manager = OSUserManager::Get();
+  DCHECK(os_user_manager);
 
   bool is_ad_user =
-      OSUserManager::Get()->IsDeviceDomainJoined() && !sam_account_name.empty();
+      os_user_manager->IsDeviceDomainJoined() && !sam_account_name.empty();
   // Login via existing AD account mapping when the device is domain joined if
   // the AD account mapping is available.
   if (is_ad_user) {
@@ -302,6 +304,14 @@ HRESULT GetUserAndDomainInfo(
       re2::RE2::FullMatch(local_account_name, "un:([^,]+)(?:,sn:([^,]+))?",
                           &username, &serial_number);
 
+      // Only collect those user names that exist on the windows device.
+      base::string16 existing_sid;
+      HRESULT hr = os_user_manager->GetUserSID(
+          OSUserManager::GetLocalDomain().c_str(),
+          base::UTF8ToUTF16(username).c_str(), &existing_sid);
+      if (FAILED(hr))
+        continue;
+
       LOGFN(VERBOSE) << "RE2 username : " << username;
       LOGFN(VERBOSE) << "RE2 serial_number : " << serial_number;
 
@@ -334,8 +344,6 @@ HRESULT GetUserAndDomainInfo(
     domain_name = OSUserManager::GetLocalDomain();
   }
 
-  OSUserManager* os_user_manager = OSUserManager::Get();
-  DCHECK(os_user_manager);
   LOGFN(VERBOSE) << "Get user sid for user " << user_name << " and domain name "
                  << domain_name;
   HRESULT hr = os_user_manager->GetUserSID(domain_name.c_str(),