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the `themeClass` property has been replaced by more general `addClass` and `removeClass` methods.

Author: jelbourn

src/cdk/overlay/overlay-container.ts

@@ -19,27 +19,29 @@ export class OverlayContainer implements OnDestroy {
 
   private _themeClass: string;
 
+  ngOnDestroy() {
+    if (this._containerElement && this._containerElement.parentNode) {
+      this._containerElement.parentNode.removeChild(this._containerElement);
+    }
+  }
+
   /**
-   * Base theme to be applied to all overlay-based components.
+   * Adds a CSS class to the overlay container.
+   * @param cssClass The CSS class to add.
    */
-  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);
-      }
+  addClass(cssClass: string) {
+    if (cssClass && cssClass.trim()) {
+      this.getContainerElement().classList.add(cssClass);
     }
-
-    this._themeClass = value;
   }
 
-  ngOnDestroy() {
-    if (this._containerElement && this._containerElement.parentNode) {
-      this._containerElement.parentNode.removeChild(this._containerElement);
+  /**
+   * Removed a CSS class from the overlay container.
+   * @param cssClass The CSS class to remove.
+   */
+  removeClass(cssClass: string) {
+    if (cssClass && cssClass.trim()) {
+      this.getContainerElement().classList.remove(cssClass);
     }
   }
 

src/cdk/overlay/overlay.md

@@ -1,3 +1,3 @@
 ### Overlay
 
-A service used to manage overlays.
+A service used to manage overlays.

src/lib/core/overlay/overlay-container.spec.ts

@@ -43,6 +43,20 @@ 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', () => {
+    const containerElement = document.querySelector('.cdk-overlay-container')!;
+
+    overlayContainer.addClass('commander-shepard');
+
+    expect(containerElement.classList.contains('commander-shepard'))
+        .toBe(true, 'Expected the overlay container to have class "commander-shepard"');
+
+    overlayContainer.removeClass('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. */