Adding Histograms for new Desktop First Run.

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index cdbc1e03a7b539b67c5c89433caa24dc467f0024..bf215051bcdc4a9a7bc030ba5ecc4bf25ca4c0ae 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -71691,6 +71691,13 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Welcome.SignInPromptResult" enum="WelcomeSignInPromptOutcome">
+  <owner>tmartino@chromium.org</owner>
+  <summary>
+    Records the result of promoting sign-in via the Welcome page.
+  </summary>
+</histogram>
+
 <histogram name="Win8.PageLoad" enum="Win8PageLoadType">
   <owner>zturner@chromium.org</owner>
   <summary>
@@ -102821,6 +102828,12 @@ value.
   <int value="1" label="Revoked ephemeral permission"/>
 </enum>
 
+<enum name="WelcomeSignInPromptOutcome" type="int">
+  <int value="0" label="User navigated away from page"/>
+  <int value="1" label="User declined prompt"/>
+  <int value="2" label="User completed sign in flow"/>
+</enum>
+
 <enum name="WhitelistedDownloadType" type="int">
   <int value="0" label="Does not match any whitelists"/>
   <int value="1" label="URL whitelist"/>