docs: add youtube to social icons (#40987)

PR Close #40987

aio/src/app/app.component.html

@@ -31,6 +31,9 @@
       <a href="https://github.com/angular/angular" title="GitHub" aria-label="Angular on github">
         <mat-icon svgIcon="logos:github"></mat-icon>
       </a>
+      <a href="https://youtube.com/angular" title="YouTube" aria-label="Angular on YouTube">
+        <mat-icon svgIcon="logos:youtube"></mat-icon>
+      </a>
     </div>
   </mat-toolbar-row>
 </mat-toolbar>

aio/src/app/app.module.ts

@@ -127,6 +127,20 @@ export const svgIconProviders = [
     },
     multi: true,
   },
+  {
+    provide: SVG_ICONS,
+    useValue: {
+      namespace: 'logos',
+      name: 'youtube',
+      svgSource:
+        '<svg focusable="false" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg">' +
+          '<path d="M21.58 7.19c-.23-.86-.91-1.54-1.77-1.77C18.25 5 12 5 12 5s-6.25 0-7.81.42c-.86.23-1.54.91-1.77 1.77' +
+            'C2 8.75 2 12 2 12s0 3.25.42 4.81c.23.86.91 1.54 1.77 1.77C5.75 19 12 19 12 19s6.25 0 7.81-.42' +
+            'c.86-.23 1.54-.91 1.77-1.77C22 15.25 22 12 22 12s0-3.25-.42-4.81zM10 15V9l5.2 3-5.2 3z" />' +
+        '</svg>',
+    },
+    multi: true,
+  },
 ];
 // tslint:enable: max-line-length
 

goldens/size-tracking/aio-payloads.json

@@ -3,7 +3,7 @@
     "master": {
       "uncompressed": {
         "runtime-es2015": 3033,
-        "main-es2015": 447766,
+        "main-es2015": 448427,
         "polyfills-es2015": 52343
       }
     }
@@ -12,7 +12,7 @@
     "master": {
       "uncompressed": {
         "runtime-es2015": 3033,
-        "main-es2015": 448055,
+        "main-es2015": 448936,
         "polyfills-es2015": 52493
       }
     }
@@ -21,7 +21,7 @@
     "master": {
       "uncompressed": {
         "runtime-es2015": 3153,
-        "main-es2015": 433285,
+        "main-es2015": 434502,
         "polyfills-es2015": 52493
       }
     }