title: Can't use MatIcon component
body: <p>I have recently updated my project to Angular v6. I am trying to install Angular Material following this guide:
  <a href="https://material.angular.io/guide/getting-started" rel="nofollow noreferrer">Material guide for Angular</a></p>
  
  <p>This is my app's module:</p>
  
  <pre class="lang-ts prettyprint-override"><code>import {MatButtonModule, MatCheckboxModule} from '@angular/material';
  import {BrowserAnimationsModule} from '@angular/platform-browser/animations';
  
  @NgModule({
   declarations: [
     AppComponent,
     PruebaComponent
   ],
   imports: [
     ...
     MatButtonModule, 
     BrowserAnimationsModule,
     MatCheckboxModule
   ],
  </code></pre>
  
  <p>This is the html of a test component:</p>
  
  <pre class="lang-html prettyprint-override"><code>&lt;h3&gt;Fab Buttons&lt;/h3&gt;
  &lt;div class="button-row"&gt;
    &lt;button mat-fab&gt;Basic&lt;/button&gt;
    &lt;button mat-fab color="primary"&gt;Primary&lt;/button&gt;
    &lt;button mat-fab color="accent"&gt;Accent&lt;/button&gt;
    &lt;button mat-fab color="warn"&gt;Warn&lt;/button&gt;
    &lt;button mat-fab disabled&gt;Disabled&lt;/button&gt;
    &lt;button mat-fab&gt;
      &lt;mat-icon aria-label="Example icon-button with a heart icon"&gt;favorite&lt;/mat-icon&gt;
    &lt;/button&gt;
    &lt;a mat-fab routerLink="."&gt;Link&lt;/a&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>However, I get this error:</p>
  
  <pre><code>compiler.js:215 Uncaught Error: Template parse errors:
  'mat-icon' is not a known element:
  1. If 'mat-icon' is an Angular component, then verify that it is part of this module.
  2. If 'mat-icon' is a Web Component then add 'CUSTOM_ELEMENTS_SCHEMA' to the '@NgModule.schemas' of this component to suppress this message. ("
  </code></pre>