feat(svg-icons): handle custom svg icons

Replace the player's default icons with custom icons.

The `experimentalSvgIcons` option accepts a `boolean` or a `string`.
If the string represents a valid svg, it will replace the default icons.

**Usage**

```javascript
import playerIcons from './asset/vjs-sprite-icons.svg';

const player = videojs('my-player', {
  experimentalSvgIcons: playerIcons,
  // ...
});
```

Or:

```javascript
const player = videojs('my-player', {
  experimentalSvgIcons: `
  <svg>
  ...
  </svg>
  `,
  // ...
});
```

- extract a `initSvgIcons_` function to activate svg icons
- add test cases

src/js/player.js

@@ -518,25 +518,7 @@ class Player extends Component {
 
     this.playbackRates(options.playbackRates);
 
-    if (options.experimentalSvgIcons) {
+    this.initSvgIcons_(options.experimentalSvgIcons);
-      // Add SVG Sprite to the DOM
-      const parser = new window.DOMParser();
-      const parsedSVG = parser.parseFromString(icons, 'image/svg+xml');
-      const errorNode = parsedSVG.querySelector('parsererror');
-
-      if (errorNode) {
-        log.warn('Failed to load SVG Icons. Falling back to Font Icons.');
-        this.options_.experimentalSvgIcons = null;
-      } else {
-        const sprite = parsedSVG.documentElement;
-
-        sprite.style.display = 'none';
-        this.el_.appendChild(sprite);
-
-        this.addClass('vjs-svg-icons-enabled');
-      }
-    }
-
     this.initChildren();
 
     // Set isAudio based on whether or not an audio tag was used
@@ -5093,6 +5075,39 @@ class Player extends Component {
     return baseOptions;
   }
 
+  /**
+   * Initialize SVG icons.
+   *
+   * @param {boolean|string} svgIconsOption
+   *        Takes a Boolean or a string as parameter, if true will activate
+   *        the default icons, if the string represents an svg it will replace
+   *        the default icons.
+   */
+  initSvgIcons_(svgIconsOption) {
+    if (!svgIconsOption) {
+      return;
+    }
+
+    const hasCustomSvgIcons = typeof svgIconsOption === 'string';
+    const svgIcons = hasCustomSvgIcons ? svgIconsOption : icons;
+    // Add SVG Sprite to the DOM
+    const parser = new window.DOMParser();
+    const parsedSVG = parser.parseFromString(svgIcons, 'image/svg+xml');
+    const errorNode = parsedSVG.querySelector('parsererror');
+
+    if (errorNode) {
+      log.warn('Failed to load SVG Icons. Falling back to Font Icons.');
+      this.options_.experimentalSvgIcons = null;
+    } else {
+      const sprite = parsedSVG.documentElement;
+
+      sprite.style.display = 'none';
+      this.el_.appendChild(sprite);
+
+      this.addClass('vjs-svg-icons-enabled');
+    }
+  }
+
   /**
    * Set debug mode to enable/disable logs at info level.
    *

test/unit/player.test.js

@@ -1000,6 +1000,39 @@ QUnit.test('should revert to font icons if the SVG sprite cannot be loaded', fun
   player.dispose();
 });
 
+QUnit.test('should add a svg-icons-enabled classname when svg icons string is valid', function(assert) {
+  // Stub a successful parsing of the SVG sprite.
+  sinon.stub(window.DOMParser.prototype, 'parseFromString').returns({
+    querySelector: () => false,
+    documentElement: document.createElement('span')
+  });
+
+  assert.expect(1);
+
+  const player = TestHelpers.makePlayer({experimentalSvgIcons: '<svg></svg>'});
+
+  assert.ok(player.hasClass('vjs-svg-icons-enabled'), 'svg-icons-enabled classname added');
+
+  window.DOMParser.prototype.parseFromString.restore();
+  player.dispose();
+});
+
+QUnit.test('should revert to font icons if the SVG sprite string is not valid', function(assert) {
+  // Stub an unsuccessful parsing of the SVG sprite.
+  sinon.stub(window.DOMParser.prototype, 'parseFromString').returns({
+    querySelector: () => true
+  });
+
+  assert.expect(1);
+
+  const player = TestHelpers.makePlayer({experimentalSvgIcons: ''});
+
+  assert.ok(!player.hasClass('vjs-svg-icons-enabled'), 'svg-icons-enabled classname was not added');
+
+  window.DOMParser.prototype.parseFromString.restore();
+  player.dispose();
+});
+
 QUnit.test('should not add a touch-enabled classname when touch is not supported', function(assert) {
   assert.expect(1);