Navi: Medium font weight for selected option in email and apps.

Screenshots in bug.

Bug: 901210
Change-Id: I7a8cc24801ac66fd2d9e01a4bae03824811dd19d
Reviewed-on: https://chromium-review.googlesource.com/c/1332715Reviewed-by: Scott Chen <scottchen@chromium.org>
Commit-Queue: Hector Carmona <hcarmona@chromium.org>
Cr-Commit-Position: refs/heads/master@{#607742}

chrome/browser/resources/welcome/onboarding_welcome/shared/chooser_shared_css.html

@@ -86,6 +86,7 @@
       .option[active] {
         border: 1px solid var(--google-blue-600);
         color: var(--google-blue-600);
+        font-weight: 500;
       }
 
       .option[active] iron-icon[icon='cr:check'] {
@@ -99,4 +100,4 @@
       }
     </style>
   </template>
-</dom-module>
\ No newline at end of file
+</dom-module>