[Drag and drop] problems when changing height after start

#### What is the expected behavior?
Drag and drop working :)

#### What is the current behavior?
If I change the height of elements (that are draggable) for example by hiding some elements **after I start dragging**, the drag and drop mechanism thinks the items are still the original height (and therefore rendering placeholder at wrong place and behaving incorrectly).

#### What are the steps to reproduce?
https://stackblitz.com/edit/angular-material2-issue-ggdtyr?file=app%2Fapp.component.css

(moving between columns does not work for some unknown reason but that is not important)

#### Which versions of Angular, Material, OS, TypeScript, browsers are affected?
newest ones

#### Is there anything else we should know?
If you point me in the right direction, I can provide a fix.

リンク先の StackBlitz の再現コード、特に app/app.component.css から始め、ドラッグ開始後に高さが変化する状態を再現します。Angular のドラッグアンドドロップのエントリポイントを追跡し、古いアイテムの寸法がプレースホルダーの配置に影響する箇所を特定します。ドラッグ中にドラッグ可能な要素の高さが変化しても、プレースホルダーとドラッグの動作が正しいままであれば完了です。

索引モデルが issue の本文から書いたものです。