Enhanced bookmarks and the DOM distiller are (or will be) used on
iOS and android. Move the function checking whether the features
are enabled into the respective component to allow sharing the code.

Move IsEnhancedBookmarksEnabled() function to the enhanced_bookmarks
component with supporting switches.

Move IsEnableDomDistillerSet() and IsEnableSyncArticlesSet() functions
to the dom_distiller component with supporting switches.

BUG=359565

Review URL: https://codereview.chromium.org/1253953002

Cr-Commit-Position: refs/heads/master@{#340526}