Implement the UI logic behind the Sign In promo in the password bubble

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 3559c46947fc6345bab802393dd2e36b66a04c87..d7006b83d167e3575ae12857263c2c64404ae695 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -37400,6 +37400,23 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="PasswordManager.SignInPromo"
+    enum="PasswordBubbleSignInPromoDismissalReason">
+  <owner>vasilii@chromium.org</owner>
+  <summary>
+    User action on the Chrome Sync promo that appears in the password bubble.
+    The promo offers to sign in to Chrome.
+  </summary>
+</histogram>
+
+<histogram name="PasswordManager.SignInPromoCountTilClick">
+  <owner>vasilii@chromium.org</owner>
+  <summary>
+    The number of times the Sign In promo in the password bubble was shown
+    before user clicked on it.
+  </summary>
+</histogram>
+
 <histogram name="PasswordManager.StorePasswordImportedFromCSVResult"
     enum="BooleanSuccess">
   <owner>xunlu@chromium.org</owner>
@@ -82754,6 +82771,12 @@ To add a new entry, add it with any value and run test to compute valid value.
   <int value="8" label="Opened automatically / Offering a password to update"/>
 </enum>
 
+<enum name="PasswordBubbleSignInPromoDismissalReason" type="int">
+  <int value="0" label="Dismissed"/>
+  <int value="1" label="Sign in"/>
+  <int value="2" label="No thanks"/>
+</enum>
+
 <enum name="PasswordFormQueryVolume" type="int">
   <int value="0" label="New password query"/>
   <int value="1" label="Current query"/>