[metrics] Change the expiry of Browser.Tabs.TotalIncompleteSwitchDuration.

The expiry is the same as Browser.Tabs.TabSwitchResult and
Browser.Tabs.TotalSwitchDuration. These metrics needs to be analyzed
together.

Fixed: 1037572
Bug: 1037572
Change-Id: I5f19e9f612361488478e7e0ff2138cae91b5cb65
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2003217
Auto-Submit: François Doray <fdoray@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Commit-Queue: François Doray <fdoray@chromium.org>
Cr-Commit-Position: refs/heads/master@{#732386}

tools/metrics/histograms/histograms.xml

@@ -20207,7 +20207,7 @@ uploading your change for review.
 </histogram>
 
 <histogram base="true" name="Browser.Tabs.TotalIncompleteSwitchDuration"
-    units="ms" expires_after="M81">
+    units="ms" expires_after="2020-06-28">
 <!-- Name completed by histogram_suffixes name="TabSwitchingType" -->
 
   <owner>fdoray@chromium.org</owner>