fix(material-experimental/mdc-slider): code review changes

* add todo to remember to add the mdc-slider back into the kitchen sink ssr app
* move _foundation.init() into the _platform.isBrowser check to avoid ssr problems

Author: wagnermaciel

src/material-experimental/mdc-slider/slider-adapter.ts

@@ -80,6 +80,8 @@ export class SliderAdapter implements MDCSliderAdapter {
     return this._delegate._getInput(thumb)._isFocused();
   }
   getThumbKnobWidth = (thumb: Thumb): number => {
+    // TODO(wagnermaciel): Check if this causes issues for SSR
+    // once the mdc-slider is added back to the kitchen sink SSR app.
     return this._delegate._getKnobElement(thumb).getBoundingClientRect().width;
   }
   getThumbBoundingClientRect = (thumb: Thumb): ClientRect => {

src/material-experimental/mdc-slider/slider.ts

@@ -151,11 +151,11 @@ export class MatSlider implements AfterViewInit, OnDestroy {
 
   ngAfterViewInit() {
     this._validateInputs();
-    this._foundation.init();
     if (this._platform.isBrowser) {
+      this._foundation.init();
       this._foundation.layout();
+      this._initialized = true;
     }
-    this._initialized = true;
   }
 
   ngOnDestroy() {