[DevTools] Add count histograms for workspace files/folders.

Bug: chromium:1447968
Change-Id: I4c79d581fc4b9272842d59d70ea85798084ea1a5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4618253
Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Auto-Submit: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1159373}

tools/metrics/histograms/metadata/dev/histograms.xml

@@ -538,6 +538,26 @@ chromium-metrics-reviews@google.com.
   </summary>
 </histogram>
 
+<histogram name="DevTools.Workspaces.NumberOfDirectoriesTraversed"
+    units="count" expires_after="M120">
+  <owner>bmeurer@chromium.org</owner>
+  <owner>hablich@chromium.org</owner>
+  <summary>
+    Number of directories within a workspace folder traversed while loading the
+    files from the folder.
+  </summary>
+</histogram>
+
+<histogram name="DevTools.Workspaces.NumberOfFilesLoaded" units="count"
+    expires_after="M120">
+  <owner>bmeurer@chromium.org</owner>
+  <owner>hablich@chromium.org</owner>
+  <summary>
+    Number of files loaded from a workspace folder (after the exclusion patterns
+    are applied).
+  </summary>
+</histogram>
+
 <histogram name="DevTools.Workspaces.PopulateWallClockTime" units="ms"
     expires_after="M120">
   <owner>bmeurer@chromium.org</owner>