Starting a refactor to allow adding metrics on 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 83839e40d228618760d0f2a79b0bf537b2462709..4883cddce0cb0cc1d9f6b896a20aaef768a040bc 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -5071,6 +5071,14 @@ 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>
@@ -50946,6 +50954,11 @@ 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"/>