Fix contextClick after multi-highlight

Summary:
Select multiple rows, and then right click, or use Ctrl-click.
This was broken, it was resetting the selection when this happened.
This fixes it.

Now after selecting multiple, what happens depends where you right-click.

If you right-click within the current selection, it stays selected and you can copy it.
But if you right-click outside the current selection, that row becomes the new selected set, and you will just be able to copy that one. This feels right to me.

Reviewed By: passy

Differential Revision: D15822668

fbshipit-source-id: 6a6cda8a8f16fec55cffa52c1c2ff958c86b3f43

src/ui/components/table/ManagedTable.js

@@ -383,11 +383,17 @@ class ManagedTable extends React.Component<
       e.button !== 0 ||
       (process.platform === 'darwin' && e.button === 0 && e.ctrlKey);
 
-    if (!contextClick) {
-      this.dragStartIndex = index;
-      document.addEventListener('mouseup', this.onStopDragSelecting);
+    if (contextClick) {
+      if (!highlightedRows.has(row.key)) {
+        highlightedRows.clear();
+        highlightedRows.add(row.key);
+      }
+      return;
     }
 
+    this.dragStartIndex = index;
+    document.addEventListener('mouseup', this.onStopDragSelecting);
+
     if (
       ((process.platform === 'darwin' && e.metaKey) ||
         (process.platform !== 'darwin' && e.ctrlKey)) &&