customtabs: UMA histogram tracking whether clients call warmup().

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 2b79ecce91a197918738cdce5151e24b370fa707..96b11a1505d03e82331f3926181fd132f919da67 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -5516,6 +5516,15 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="CustomTabs.WarmupStateOnLaunch" enum="WarmupStateOnLaunch">
+  <owner>lizeb@chromium.org</owner>
+  <summary>
+    Recorded only on Android. Reports whether warmup() has been called when a
+    Custom Tabs Intent is received from an application, and if so, whether the
+    call could be matched with a session.
+  </summary>
+</histogram>
+
 <histogram name="DataReductionProxy.AutoLoFiAccuracy"
     enum="DataReductionProxyAutoLoFiAccuracy">
   <owner>bengr@chromium.org</owner>
@@ -73441,6 +73450,14 @@ To add a new entry, add it with any value and run test to compute valid value.
   <int value="5" label="Policy"/>
 </enum>
 
+<enum name="WarmupStateOnLaunch" type="int">
+  <int value="0" label="No Session, No Warmup"/>
+  <int value="1" label="No Session, Warmup"/>
+  <int value="2" label="Session, No Warmup, Warmup called from another UID"/>
+  <int value="3" label="Session, No Warmup"/>
+  <int value="4" label="Session, Warmup"/>
+</enum>
+
 <enum name="WebBluetoothConnectGATTOutcome" type="int">
   <int value="0" label="Success"/>
   <int value="1" label="Device no longer in range"/>