GitLab

 - Moving ComponentsDomHandler to its own .h/cc files,
   and renaming to ComponentsHandler.
 - Moving some logic from ComponentsUI to ComponentsHandler so that proper
   lifetime methods (OnJavascriptAllowed/Disallowed) can be leveraged.

This is in preparation of migrating this page to JS modules.

Bug: 1028829
Change-Id: I530c439b3e659f3b1b5e5dc3ef05f2a3df88559e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1939893
Commit-Queue: Demetrios Papadopoulos <dpapad@chromium.org>
Reviewed-by: Sorin Jianu <sorin@chromium.org>
Reviewed-by: Rebekah Potter <rbpotter@chromium.org>
Auto-Submit: Demetrios Papadopoulos <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#722633}