feat(overlay): replace OverlayContainer themeClass w/ addClass/removeClass methods

BREAKING CHANGE: Now that the Overlay is part of the cdk rather than Angular Material directly,
the `themeClass` property has been removed. To add a class to the
overlay for theming, you can do
```ts
overlayContainer.getContainerElement().classList.add('my-theme-class');
```

Author: jelbourn

guides/theming.md

@@ -169,7 +169,7 @@ Since certain components (e.g. menu, select, dialog, etc.) are inside of a globa
 an additional step is required for those components to be affected by the theme's css class selector
 (`.unicorn-dark-theme` in the example above).
 
-To do this, you can specify a `themeClass` on the global overlay container. For the example above,
+To do this, you can add the approviate class to the global overlay container. For the example above,
 this would look like:
 ```ts
 import {OverlayContainer} from '@angular/material';
@@ -179,7 +179,7 @@ import {OverlayContainer} from '@angular/material';
 })
 export class UnicornCandyAppModule {
   constructor(overlayContainer: OverlayContainer) {
-    overlayContainer.themeClass = 'unicorn-dark-theme';
+    overlayContainer.getContainerElement().classList.add('unicorn-dark-theme');
   }
 }
 ```

src/cdk/overlay/overlay-container.spec.ts

@@ -26,6 +26,10 @@ describe('OverlayContainer', () => {
     overlayContainer = oc;
   }));
 
+  afterEach(() => {
+    overlayContainer.ngOnDestroy();
+  });
+
   it('should remove the overlay container element from the DOM on destruction', () => {
     const fixture = TestBed.createComponent(TestComponentWithTemplatePortals);
 
@@ -43,6 +47,19 @@ describe('OverlayContainer', () => {
     expect(document.querySelector('.cdk-overlay-container'))
         .toBeNull('Expected the overlay container *not* to be in the DOM after destruction');
   });
+
+  it('should add and remove css classes from the container element', () => {
+    overlayContainer.getContainerElement().classList.add('commander-shepard');
+
+    const containerElement = document.querySelector('.cdk-overlay-container')!;
+    expect(containerElement.classList.contains('commander-shepard'))
+        .toBe(true, 'Expected the overlay container to have class "commander-shepard"');
+
+    overlayContainer.getContainerElement().classList.remove('commander-shepard');
+
+    expect(containerElement.classList.contains('commander-shepard'))
+        .toBe(false, 'Expected the overlay container not to have class "commander-shepard"');
+  });
 });
 
 /** Test-bed component that contains a TempatePortal and an ElementRef. */

src/cdk/overlay/overlay-container.ts

@@ -17,34 +17,14 @@ import {Injectable, Optional, SkipSelf, OnDestroy} from '@angular/core';
 export class OverlayContainer implements OnDestroy {
   protected _containerElement: HTMLElement;
 
-  private _themeClass: string;
-
-  /**
-   * Base theme to be applied to all overlay-based components.
-   */
-  get themeClass(): string { return this._themeClass; }
-  set themeClass(value: string) {
-    if (this._containerElement) {
-      if (this._themeClass) {
-        this._containerElement.classList.remove(this._themeClass);
-      }
-
-      if (value) {
-        this._containerElement.classList.add(value);
-      }
-    }
-
-    this._themeClass = value;
-  }
-
   ngOnDestroy() {
     if (this._containerElement && this._containerElement.parentNode) {
       this._containerElement.parentNode.removeChild(this._containerElement);
     }
   }
 
   /**
-   * This method returns the overlay container element.  It will lazily
+   * This method returns the overlay container element. It will lazily
    * create the element the first time  it is called to facilitate using
    * the container in non-browser environments.
    * @returns the container element
@@ -62,10 +42,6 @@ export class OverlayContainer implements OnDestroy {
     let container = document.createElement('div');
     container.classList.add('cdk-overlay-container');
 
-    if (this._themeClass) {
-      container.classList.add(this._themeClass);
-    }
-
     document.body.appendChild(container);
     this._containerElement = container;
   }

src/cdk/overlay/overlay.spec.ts

@@ -469,44 +469,6 @@ describe('Overlay', () => {
   });
 });
 
-describe('OverlayContainer theming', () => {
-  let overlayContainer: OverlayContainer;
-  let overlayContainerElement: HTMLElement;
-
-  beforeEach(async(() => {
-    TestBed.configureTestingModule({ imports: [OverlayContainerThemingTestModule] });
-    TestBed.compileComponents();
-  }));
-
-  beforeEach(inject([OverlayContainer], (o: OverlayContainer) => {
-    overlayContainer = o;
-    overlayContainerElement = overlayContainer.getContainerElement();
-  }));
-
-  afterEach(() => {
-    overlayContainerElement.parentNode!.removeChild(overlayContainerElement);
-  });
-
-  it('should be able to set a theme on the overlay container', () => {
-    overlayContainer.themeClass = 'my-theme';
-    expect(overlayContainerElement.classList).toContain('my-theme');
-  });
-
-  it('should clear any previously-set themes when a new theme is set', () => {
-    overlayContainer.themeClass = 'initial-theme';
-    expect(overlayContainerElement.classList).toContain('initial-theme');
-
-    overlayContainer.themeClass = 'new-theme';
-    expect(overlayContainerElement.classList).not.toContain('initial-theme');
-    expect(overlayContainerElement.classList).toContain('new-theme');
-  });
-
-  it('should not throw when switching from a blank theme', () => {
-    overlayContainer.themeClass = '';
-    expect(() => overlayContainer.themeClass = 'new-theme').not.toThrow();
-  });
-});
-
 /** Simple component for testing ComponentPortal. */
 @Component({
   selector: 'pizza',