title: Angular 6 - mat-icon-rtl-mirror is not rendering the icon
body: <p>I am implementing tree navigation using the documentation from the official angular material site. When using 'mat-icon-rtl-mirror' CSS class to render an icon, the browser is showing the name of the icon rather than the actual image.</p>
  
  <pre><code>&lt;mat-icon class="mat-icon-rtl-mirror"&gt;
        {{treeControl.isExpanded(node) ? 'expand_more' : 'chevron_right'}}
  &lt;/mat-icon&gt;
  </code></pre>
  
  <p>The result I am getting is like this</p>
  
  <p><a href="https://i.stack.imgur.com/sdhbf.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/sdhbf.png" alt="enter image description here"></a></p>
  
  <p>When really it should be like this</p>
  
  <p><a href="https://i.stack.imgur.com/9lZwZ.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/9lZwZ.png" alt="enter image description here"></a></p>
  
  <p>I am also attaching my app.module.ts</p>
  
  <pre><code>import { BrowserModule } from '@angular/platform-browser';
  import { NgModule } from '@angular/core';
  import { HttpClientModule } from '@angular/common/http';
  
  import { AppComponent } from './app.component';
  
  import {FormsModule, ReactiveFormsModule} from '@angular/forms';
  import { MatButtonModule, MatCheckboxModule, MatIconModule} from '@angular/material';
  import {platformBrowserDynamic} from '@angular/platform-browser-dynamic';
  import {BrowserAnimationsModule} from '@angular/platform-browser/animations';
  import {DemoMaterialModule} from '../material-module';
  import { MatTreeModule } from '@angular/material/tree';
  
  import {TreeChecklistExample} from './asset-navigation/asset-navigation';
  
  @NgModule({
    declarations: [
      AppComponent,
      TreeChecklistExample
    ],
    imports: [
      BrowserModule,
      BrowserAnimationsModule,
      FormsModule,
      HttpClientModule,
      DemoMaterialModule,
      ReactiveFormsModule,
      MatButtonModule, 
      MatCheckboxModule, 
      MatTreeModule, 
      MatIconModule
    ],
    providers: [],
    bootstrap: [AppComponent]
  })
  export class AppModule { }
  </code></pre>
  
  <p>How do I fix this ?</p>