mat-select seems to have serious performance issue

#### Bug, feature request, or proposal:
With latest release, mat-form-field support was added for mat-select. But it introduced performance issues when we have multiple select lists (5-8).

When we use mat-form-field with input or text area it doesn't seem to cause any performance issue but it seem that its implementation for mat-select needs a review. On lengthy forms we are seeing a delay of up to 3 seconds, which are instant without mat-form-field on mat-select.

#### What is the expected behavior?
It should smooth and fast.

#### What is the current behavior?
Its very slow.

#### Which versions of Angular, Material, OS, TypeScript, browsers are affected?
Angular 4.4.4
Material 2.0.0-beta.12
Chrome

报告提到了 mat-select 和 mat-form-field，但没有提供文件、测试或复现入口。首先，在 Angular 4.4.4 和 Material 2.0.0-beta.12 下使用 5–8 个 mat-select 控件复现报告中的延迟，然后将其与不使用 mat-form-field 的 mat-select 进行比较。完成标准是：长表单不再出现报告中所述的数秒延迟，并且该行为由回归测试或基准测试覆盖。

由索引模型根据 Issue 内容生成。