Calculate column widths on attach

src/vaadin-grid.html

@@ -415,6 +415,15 @@
         this.addEventListener('animationend', this._onAnimationEnd);
       }
 
+      connectedCallback() {
+        super.connectedCallback();
+        requestAnimationFrame(() => {
+          if (this._recalculateColumnWidthOnceLoadingFinished) {
+            this.recalculateColumnWidths();
+          }
+        });
+      }
+
       __hasRowsWithClientHeight() {
         return !!Array.from(this.$.items.children).filter(row => row.clientHeight).length;
       }

test/column-auto-width.html

@@ -92,7 +92,7 @@
             );
           });
         };
-
+        grid._recalculateColumnWidths.called = false;
         whenColumnWidthsCalculated(() => {
           expectColumnWidthsToBeOk(columns);
           done();
@@ -106,6 +106,7 @@
         requestAnimationFrame(() => {
           grid.hidden = false;
 
+          grid._recalculateColumnWidths.called = false;
           whenColumnWidthsCalculated(() => {
             expectColumnWidthsToBeOk(columns);
             done();