New metric to track usage of the new GAIA flow.

BUG=464051

Review URL: https://codereview.chromium.org/1009453003

Cr-Commit-Position: refs/heads/master@{#320880}

chrome/browser/ui/webui/chromeos/login/gaia_screen_handler.cc

@@ -121,6 +121,11 @@ void RecordSAMLScrapingVerificationResultInHistogram(bool success) {
   UMA_HISTOGRAM_BOOLEAN("ChromeOS.SAML.Scraping.VerificationResult", success);
 }
 
+void RecordGAIAFlowTypeHistogram() {
+  UMA_HISTOGRAM_BOOLEAN("ChromeOS.GAIA.WebViewFlow",
+                        StartupUtils::IsWebviewSigninEnabled());
+}
+
 // The Task posted to PostTaskAndReply in StartClearingDnsCache on the IO
 // thread.
 void ClearDnsCache(IOThread* io_thread) {
@@ -422,6 +427,8 @@ void GaiaScreenHandler::HandleCompleteAuthentication(
   if (!Delegate())
     return;
 
+  RecordGAIAFlowTypeHistogram();
+
   DCHECK(!email.empty());
   DCHECK(!gaia_id.empty());
   const std::string sanitized_email = gaia::SanitizeEmail(email);
@@ -438,6 +445,8 @@ void GaiaScreenHandler::HandleCompleteAuthenticationAuthCodeOnly(
   if (!Delegate())
     return;
 
+  RecordGAIAFlowTypeHistogram();
+
   UserContext user_context;
   user_context.SetAuthFlow(UserContext::AUTH_FLOW_EASY_BOOTSTRAP);
   user_context.SetAuthCode(auth_code);
@@ -579,6 +588,7 @@ void GaiaScreenHandler::DoCompleteLogin(const std::string& gaia_id,
 
   if (using_saml && !using_saml_api_)
     RecordSAMLScrapingVerificationResultInHistogram(true);
+  RecordGAIAFlowTypeHistogram();
 
   DCHECK(!typed_email.empty());
   DCHECK(!gaia_id.empty());

tools/metrics/histograms/histograms.xml

@@ -2782,6 +2782,14 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="ChromeOS.GAIA.WebViewFlow" enum="BooleanGAIAWebViewFlow">
+  <owner>ginkage@chromium.org</owner>
+  <summary>
+    Whether a user signed in using the new WebView-based GAIA flow. This value
+    is sent after the GAIA screen has completed user authentication.
+  </summary>
+</histogram>
+
 <histogram name="ChromeOS.MachineIdRegen.AgeSeconds" units="seconds">
   <owner>zeuthen@chromium.org</owner>
   <summary>
@@ -45023,6 +45031,11 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <int value="1" label="Force Disabled"/>
 </enum>
 
+<enum name="BooleanGAIAWebViewFlow" type="int">
+  <int value="0" label="iframe-based flow"/>
+  <int value="1" label="WebView-based flow"/>
+</enum>
+
 <enum name="BooleanHadBlankText" type="int">
   <int value="0" label="Did not have blank text"/>
   <int value="1" label="Had blank text"/>