[ios] Add MW configuration metrics.

Add enum histogram for ios multi-window configuration
recording. Each minute one bucket from the enum will
be increased by 1.

Code is in: https://chromium-review.googlesource.com/c/chromium/src/+/2445415

Bug: 1134568
Change-Id: I418120cc33c8f866b1dea4c2800493160179fcb5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2445491Reviewed-by: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Mark Cogan <marq@chromium.org>
Commit-Queue: David Jean <djean@chromium.org>
Cr-Commit-Position: refs/heads/master@{#818376}

tools/metrics/histograms/enums.xml

@@ -38732,6 +38732,23 @@ Called by update_gpu_driver_bug_workaround_entries.py.-->
   <int value="6" label="Most Visited Entry"/>
 </enum>
 
+<enum name="IOSMultiWindowConfiguration">
+  <int value="0" label="Unspecified"/>
+  <int value="1" label="Fullscreen"/>
+  <int value="2" label="Fullscreen with Slideover"/>
+  <int value="3" label="Shared Standard"/>
+  <int value="4" label="Shared Standard with Slideover"/>
+  <int value="5" label="Shared Compact"/>
+  <int value="6" label="Shared Compact with Slideover"/>
+  <int value="7" label="Slideover"/>
+  <int value="8" label="Standard beside Standard"/>
+  <int value="9" label="Standard beside Standard with Slideover"/>
+  <int value="10" label="Standard beside Compact"/>
+  <int value="11" label="Standard beside Compact with Slideover"/>
+  <int value="12" label="Compact beside Compact"/>
+  <int value="13" label="Compact beside Compact with Slideover"/>
+</enum>
+
 <enum name="IOSNTPImpression">
   <int value="0" label="Local suggestions"/>
   <int value="1" label="Remote suggestions"/>

tools/metrics/histograms/histograms_xml/ios/histograms.xml

@@ -495,6 +495,13 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
   </summary>
 </histogram>
 
+<histogram name="IOS.MultiWindow.Configuration"
+    enum="IOSMultiWindowConfiguration" expires_after="2021-06-30">
+  <owner>marq@chromium.org</owner>
+  <owner>djean@chromium.org</owner>
+  <summary>MultiWindow configration sampled once per minute.</summary>
+</histogram>
+
 <histogram name="IOS.MultiWindow.OpenInNewWindow" enum="WindowActivityOrigin"
     expires_after="2021-06-30">
   <owner>marq@chromium.org</owner>