Set min/max width on content cells

For table cells, setting the width css attribute isn’t sufficient to
prevent them from shrinking. Set min and max width.

Change-Id: I02592a8e41f55a9f250cee2735c4cc7ec9566e09

polygerrit-ui/app/elements/diff/gr-diff/gr-diff.html

diff --git a/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.html b/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.html
index f32454d..1e7b0e4 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.html
+++ b/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.html
@@ -92,7 +92,10 @@
       }
       .content {
         overflow: hidden;
-        width: var(--content-width, 80ch);
+        /* Set max and min width since setting width on table cells still
+           allows them to shrink. */
+        max-width: var(--content-width, 80ch);
+        min-width: var(--content-width, 80ch);
       }
       .content.left {
         -webkit-user-select: var(--left-user-select, text);