Implement newly designed sign-in related histograms for desktop platorms.

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 90399295a5694f605ac20e402e6e831627c16471..4dd6fda2b7a3171c631d863d97ef13d0974aced5 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -44105,6 +44105,11 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Signin.SigninCompletedAccessPoint" enum="SigninAccessPoint">
+  <owner>gogerald@chromium.org</owner>
+  <summary>Logs the original access point that completed the sign in.</summary>
+</histogram>
+
 <histogram name="Signin.SigninSource" enum="SigninSource">
   <owner>noms@chromium.org</owner>
   <summary>
@@ -44113,6 +44118,14 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Signin.SigninStartedAccessPoint" enum="SigninAccessPoint">
+  <owner>gogerald@chromium.org</owner>
+  <summary>
+    Logs the original access point that displayed the signin or reauth Gaia
+    page, before the page is displayed.
+  </summary>
+</histogram>
+
 <histogram name="Signin.SignoutProfile" enum="SigninSignoutProfile">
   <owner>mlerman@chromium.org</owner>
   <summary>Track how a profile gets signed out.</summary>
@@ -75028,6 +75041,26 @@ To add a new entry, add it with any value and run test to compute valid value.
   <int value="2" label="Dismiss"/>
 </enum>
 
+<enum name="SigninAccessPoint" type="int">
+  <int value="0" label="Start page"/>
+  <int value="1" label="NTP Link"/>
+  <int value="2" label="Menu"/>
+  <int value="3" label="Settings"/>
+  <int value="4" label="Supervised user"/>
+  <int value="5" label="Extension install bubble"/>
+  <int value="6" label="Extensions"/>
+  <int value="7" label="Apps page link"/>
+  <int value="8" label="Bookmark bubble"/>
+  <int value="9" label="Bookmark manager"/>
+  <int value="10" label="Avatar bubble sign in"/>
+  <int value="11" label="User manager"/>
+  <int value="12" label="Devices page"/>
+  <int value="13" label="Cloud print"/>
+  <int value="14" label="Content area"/>
+  <int value="15" label="Signin promo"/>
+  <int value="16" label="Recent tabs"/>
+</enum>
+
 <enum name="SigninAccountReconcilorState" type="int">
   <int value="0" label="OK">
     The account reconcilor has finished running and is up-to-date.