Record document mode histogram in UMA on every upload.

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 0976bd9367e5947143a1caa2253b9523a6cf210f..8a9d179146e73da93a00b10ab55c9ab9f2b952d0 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -4954,6 +4954,14 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <summary>Result of DNS probes sent by the probe service.</summary>
 </histogram>
 
+<histogram name="DocumentActivity.Enabled" enum="RunningMode">
+  <owner>mariakhomenko@chromium.org</owner>
+  <summary>
+    Recorded only for Android. Records on every metrics upload whether document
+    mode is enabled.
+  </summary>
+</histogram>
+
 <histogram name="DomainBoundCerts.DBLoadedCount">
   <owner>mattm@chromium.org</owner>
   <summary>Number of certs loaded from domain bound cert database.</summary>
@@ -50163,6 +50171,11 @@ To add a new entry, add it with any value and run test to compute valid value.
   <int value="12" label="Import resource"/>
 </enum>
 
+<enum name="RunningMode" type="int">
+  <int value="0" label="Document Mode"/>
+  <int value="1" label="Tabbed Mode"/>
+</enum>
+
 <enum name="SavePasswordPromptResponseType" type="int">
   <int value="0" label="NO_RESPONSE"/>
   <int value="1" label="REMEMBER_PASSWORD"/>