[conversions] Add scrollbars around tables for small width screens

Adds overflox-x:scroll to the css for the containers which wrap the
tables on the chrome://conversion-internals page. This stops the
table from rendering outside the bounds of container on narrow screens.

Bug: 1132929
Change-Id: If99697c784516ac9c0c8a004646ef29695b31683
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2436290
Commit-Queue: John Delaney <johnidel@chromium.org>
Reviewed-by: Charlie Harrison <csharrison@chromium.org>
Cr-Commit-Position: refs/heads/master@{#811527}

content/browser/resources/conversions/conversion_internals.css

@@ -36,6 +36,7 @@ body {
   border: 1px solid #cecece;
   border-radius: 3px;
   line-height: 1.5;
+  overflow-x: scroll;
   padding: 19px;
 }