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

ui/webui/resources/js/cr/ui/list.js

Index: ui/webui/resources/js/cr/ui/list.js
diff --git a/ui/webui/resources/js/cr/ui/list.js b/ui/webui/resources/js/cr/ui/list.js
index 99196c6a1a37d87cbf73f0a5afdc2d45ce991418..e3015d5fcc71466f47120931c90de02f9d8b4781 100644
--- a/ui/webui/resources/js/cr/ui/list.js
+++ b/ui/webui/resources/js/cr/ui/list.js
@@ -325,6 +325,7 @@ cr.define('cr.ui', function() {
       this.addEventListener('blur', this.handleElementBlur_, true);
       this.addEventListener('scroll', this.handleScroll.bind(this));
       this.setAttribute('role', 'list');
+      this.onClientWidthChangedCallback_ = null;
 
       // Make list focusable
       if (!this.hasAttribute('tabindex'))
@@ -1058,6 +1059,13 @@ cr.define('cr.ui', function() {
       return height;
     },
 
+    setClientWidthChangedCallback: function(callback) {
+      this.onClientWidthChangedCallback_ = callback;
+    },
+
+    // Memorize the last clientWidth to trigger onClientWidthChanged callback.
+    oldClientWidth: -1,
+
     /**
      * Redraws the viewport.
      */
@@ -1072,6 +1080,11 @@ cr.define('cr.ui', function() {
         this.lastIndex_ = 0;
         this.remainingSpace_ = this.clientHeight != 0;
         this.mergeItems(0, 0);
+        if (this.clientWidth != this.oldClientWidth &&
+            this.onClientWidthChangedCallback_) {
+          this.oldClientWidth = this.clientWidth;
+          this.onClientWidthChangedCallback_(this.clientWidth);
+        }
         return;
       }
 
@@ -1116,6 +1129,11 @@ cr.define('cr.ui', function() {
       }
 
       this.mergeItems(firstIndex, lastIndex);
+      if (this.clientWidth != this.oldClientWidth &&
+          this.onClientWidthChangedCallback_) {
+        this.oldClientWidth = this.clientWidth;
+        this.onClientWidthChangedCallback_(this.clientWidth);
+      }
 
       if (!this.pinnedItem_ && this.cachedItems_[leadIndex] &&
           this.cachedItems_[leadIndex].parentNode == this) {