Use actual client width of list excluding scroll bar for adjusting column widths.

ui/webui/resources/js/cr/ui/table.js

Index: ui/webui/resources/js/cr/ui/table.js
diff --git a/ui/webui/resources/js/cr/ui/table.js b/ui/webui/resources/js/cr/ui/table.js
index 9e28e4c752e2361270ae2a7e037db70ffea79ea0..ec50933e83ed06f3936590a28b93aa25c5b9fee5 100644
--- a/ui/webui/resources/js/cr/ui/table.js
+++ b/ui/webui/resources/js/cr/ui/table.js
@@ -192,7 +192,16 @@ cr.define('cr.ui', function() {
      * Redraws the table.
      */
     redraw: function() {
+      var widthBeforeUpdate = this.list_.clientWidth;
       this.list_.redraw();
+      // When resizing the window, vertical scrollbar might appear/disappear
+      // based on the balance between the view size and # of items. This logic
+      // is placed here instead of resize() because clientWidth is updated
+      // after drawing.
+      if (this.list_.clientWidth != widthBeforeUpdate) {
+        this.normalizeColumns();
+        this.list_.redraw();
+      }
       this.header_.redraw();
     },
 
@@ -202,7 +211,15 @@ cr.define('cr.ui', function() {
     },
 
     endBatchUpdates: function() {
+      var widthBeforeUpdate = this.list_.clientWidth;
       this.list_.endBatchUpdates();
+      // Update of the list content may change the client width of the list
+      // because vertical scrollbar might appear/disappear depending on the
+      // number of items.
+      if (this.list_.clientWidth != widthBeforeUpdate) {
+        this.normalizeColumns();
+        this.list_.redraw();
+      }
       this.header_.endBatchUpdates();
     },
 
@@ -361,7 +378,9 @@ cr.define('cr.ui', function() {
     },
 
     normalizeColumns: function() {
-      this.columnModel.normalizeWidths(this.clientWidth);
+      // list_.clientWidth must be used here instead of this.clientWidth,
+      // because it can be narrower by the thickness of the vertical scrollbar.
+      this.columnModel.normalizeWidths(this.list_.clientWidth);

[yamaguchi, 2017/03/14 09:07:30]

cr.ui.table.TableColumnModel.normalizeWidths only changes the first column.
A good point with it is that it doesn't cause column size drift even when
repeatedly flipping the scroll bar on/off.
Downside of it is that the it shrinks the first column which shows the file
names (relatively important information) in case of the Files app.

Another option would be to resize all columns keeping the ratio.

     }
   };