Add the missing Mark-Compact GC phase histogram.

This adds V8.GCFinalizeMC.Evacuate histogram that was not included in
the previous CL by mistake:
https://chromium-review.googlesource.com/c/chromium/src/+/1095156

Bug: chromium:850508
Change-Id: I309e6de32ae64cdd727480b014ad533920709512
Reviewed-on: https://chromium-review.googlesource.com/1105817Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#570706}

tools/metrics/histograms/histograms.xml

@@ -105219,6 +105219,15 @@ uploading your change for review.
   </summary>
 </histogram>
 
+<histogram name="V8.GCFinalizeMC.Evacuate" units="ms">
+  <owner>ulan@chromium.org</owner>
+  <owner>hpayer@chromium.org</owner>
+  <summary>
+    Time spent in the evacuation phase of incremental latency-optimized
+    Mark-Compact GC.
+  </summary>
+</histogram>
+
 <histogram name="V8.GCFinalizeMC.Finish" units="ms">
   <owner>ulan@chromium.org</owner>
   <owner>hpayer@chromium.org</owner>