Fix intervention flags table width for tablet.

Before screenshot:
https://drive.google.com/file/d/16YllngmNnAqhAv-9BfRTeJZ3GPQPTzG9

After screenshot:
https://drive.google.com/file/d/1TcfLwcwlm-odd05KfHyHwuDDrsVvC1VZ

Bug: 798874
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I38608bf5ccb5baac4939fc44a8567af4879086f5
Reviewed-on: https://chromium-review.googlesource.com/848356Reviewed-by: Ryan Sturm <ryansturm@chromium.org>
Commit-Queue: Thanh Le <thanhdle@chromium.org>
Cr-Commit-Position: refs/heads/master@{#527063}

chrome/browser/resources/interventions_internals/index.css

@@ -273,7 +273,7 @@ tr.expansion-row td:nth-child(odd) {
   }
 
   #previews-flags-table {
-    width: 30%;
+    width: 60%;
   }
 
   .log-time {