feat(tabs): md-stretch-tabs (#1909)

Stretch tabs grow until they fill the tab group width.

Closes #1353

src/demo-app/tabs/tabs-demo.html

@@ -97,6 +97,15 @@
   </md-tab>
 </md-tab-group>
 
+<h1>Stretched Tabs</h1>
+
+<md-tab-group class="demo-tab-group" style="height: 200px" md-stretch-tabs>
+  <md-tab *ngFor="let tab of tabs" [disabled]="tab.disabled">
+    <template md-tab-label>{{tab.label}}</template>
+    {{tab.content}}
+  </md-tab>
+</md-tab-group>
+
 
 <h1>Async Tabs</h1>
 

src/lib/tabs/tab-group.scss

@@ -25,6 +25,11 @@
   }
 }
 
+:host[md-stretch-tabs] .md-tab-label {
+  flex-basis: 0;
+  flex-grow: 1;
+}
+
 // The ink bar that displays next to the active tab
 md-ink-bar {
   @include ink-bar;