Snackbar for promoting Data Saver to existing users

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 0fdeeb1de72d951a07241bc23f21cb28593dbcd5..8c2951f2286281786ed1695a1e7c4d050fb78852 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -8741,6 +8741,16 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="DataReductionProxy.SnackbarPromo.DataSavings" units="MB">
+  <owner>bengr@chromium.org</owner>
+  <owner>megjablon@chromium.org</owner>
+  <summary>
+    Logs the data savings in MB of the data reduction proxy snackbar promo that
+    was shown. The snackbar promo shows the user the amount of data Chrome has
+    saved them using Data Saver.
+  </summary>
+</histogram>
+
 <histogram name="DataReductionProxy.StartupState"
     enum="DataReductionProxyStartupState">
   <owner>bengr@chromium.org</owner>
@@ -8780,15 +8790,15 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <owner>bengr@chromium.org</owner>
   <owner>megjablon@chromium.org</owner>
   <summary>
-    Samples of user interactions with the Data Reduction Proxy promo, First Run
+    Samples of user interactions with the Data Reduction Proxy promos, First Run
     Experience, and settings menu. All samples are mutually exclusive. These
     samples include:
 
-    The user interactions with the promo. On Android, there are three actions
-    that dismiss the promo (enable, dismiss, and learn more) and on iOS there is
-    a toggle to enable the proxy. This is sampled when the promo leaves view. If
-    the user clicks the link to the settings menu, the state of the ON/OFF
-    switch in the menu is sampled when the view is exited.
+    The user interactions with the second run promo. On Android, there are three
+    actions that dismiss this promo (enable, dismiss, and learn more) and on iOS
+    there is a toggle to enable the proxy. This is sampled when the promo leaves
+    view. If the user clicks the link to the settings menu, the state of the
+    ON/OFF switch in the menu is sampled when the view is exited.
 
     Any other user interaction with the the ON/OFF switch in the settings menu
     for reducing data usage. Only the setting changes between entering the
@@ -8805,6 +8815,10 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
     The user interactions with the Infobar promo. On Android, there are two
     actions that dismiss the promo (enable, dismiss). This is sampled when the
     promo leaves view.
+
+    The user interactions with the Snackbar promo. The user can either ignore
+    the promo or click the action to the Settings menu. From the settings menu,
+    the user may enable or disable the proxy.
   </summary>
 </histogram>
 
@@ -78095,6 +78109,12 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <int value="10" label="Disabled directly from the First Run Experience"/>
   <int value="11" label="Enabled directly from the Infobar promo"/>
   <int value="12" label="InfoBar promo dismissed (proxy not enabled)"/>
+  <int value="13"
+      label="Snackbar promo link clicked, but no action was taken (the proxy
+             remained enabled)"/>
+  <int value="14"
+      label="Snackbar promo link clicked, and the proxy was disabled"/>
+  <int value="15" label="Snackbar promo dismissed (no action taken)"/>
 </enum>
 
 <enum name="DataUsageReportSubmissionResult" type="int">
@@ -99247,6 +99267,7 @@ value.
   <int value="13" label="DOWNLOAD_DELETE_UNDO"/>
   <int value="14" label="SPECIAL_LOCALE"/>
   <int value="15" label="BLIMP"/>
+  <int value="16" label="DATA_REDUCTION_PROMO"/>
 </enum>
 
 <enum name="SnippetOpenMethod" type="int">