Make generated field groups inherit from RefCountedCopyable.

Currently generated groups such as StyleSurroundData inherit from
RefCounted, which means we have to explicitly specify a copy
constructor. Inheriting from RefCountedCopyable instead means we can
just use the compiler generated copy constructor.

Diff of generated files:
https://gist.github.com/darrnshn/b3f3492858caedc6359a0507dc173dff/revisions

BUG=628043

Review-Url: https://codereview.chromium.org/2799363002
Cr-Commit-Position: refs/heads/master@{#467262}
1 file changed